A. testudinalis. This species is found in vast numbers all along the New England shore, clinging to the rocks between tides. They are usually called limpets. The shell is solid, conical, with an oval outline, and with no trace of a spiral form in the adult. When the shell is thoroughly cleaned, it generally presents a mottled coloration of pale green, brown, and white. Inside it is white and nacreous, with a large brown [pg357] area under the apex. The animal has a powerful foot, by means of which it is enabled to cling to a rock with great strength. In order to dislodge it, it is necessary to approach carefully, and, taking the creature unawares, quickly slip a broad knife-blade under the foot, otherwise it is quite impossible to tear it from its resting-place. A. testudinalis lives entirely between tides, and ranges from the northernmost waters to New York. It feeds upon algæ and is a very sluggish animal. It has been said to leave its resting-place and wander about in search of food, returning to its original and usual spot when the tide begins to ebb. (Page 343.)
A. testudinalis, variety alveus. This variety is smaller, more fragile, and oblong. It lives upon eel-grass, its oblong shell being adapted to the narrow leaves of the grass. The coloration is brighter—reddish-brown spots on a white surface. It is exceedingly common on the New England coast.
A. mitra. On the Pacific coast there are a number of acmæas. A. mitra is often found dead upon the beaches. It is conical in form and pure creamy-white in color. It looks very much like a clown's pointed cap.
A. patina. This is also very abundant in California. Outside it is dark in color and is often incrusted with mineral deposits. Within there is a dark ring around the edge, then a zone of bluish-white, and a patch of brown just beneath the apex.
Genus Lottia
L. gigantea. This is the largest of the California limpets. Specimens three inches long have been found. The outer surface of the shell is rough and brownish in color. The apex is near one end. Within it is almost black, shining, lustrous, with a horseshoe-shaped muscle-scar under the apex. The color is bluish and brown. (Plate LXV.)
Family FISSURELLIDÆ
This is an extensive family, including several genera and a number of species, commonly known as keyhole-limpets. In the general form of the shell they closely resemble the true limpets, the Acmæidæ, except that they have a hole, or rather a slit, in the shell just back of the apex. Often this slit is so long that it has entirely removed the apex of the conical shell.
Genus Fissurella
F. alternata, F. barbadensis. These species occur upon the southern shores of the United States, the latter, however, being confined to [pg358] extreme southern Florida. F. barbadensis has heavy longitudinal ribs and is light green within, with a rosy circle about the apical perforation. (Plate LXV.)
Genus Glyphis
G. aspersa. One of the numerous species belonging to this family which are found on the west coast of the United States. It is about one and a half inches long, grayish-white, with sharply raised longitudinal ridges, slightly rayed, crossed by revolving ribs, which give to the outer surface a decussated appearance. The apex is forward of the center, and is entirely replaced by a round perforation. The edge is wrinkled, and within smooth and white.
Genus Lucapina
L. crenulata. The largest of the keyhole-limpets; the shell is often four inches in length, while the animal, with its huge yellowish foot and dark-colored mantle, which is thrown back, almost concealing the shell upon its back, is much larger. The apical perforation is very large. Shell flattened, with radiating, rounded, crowded ribs; brownish-white in color; edge crenulated; within pure white. It is found at Monterey, but live specimens are not very frequently seen near the beach. (Plate LXVI.)
Family HALIOTIDÆ
Genus Haliotis
This family is closely allied to the Fissurellidæ. The species are known on the Pacific coast by the name of abalone shells, and in England and the Channel Islands as ormers or sea-ears. There are no species of Haliotis on the east coast of the United States, but one has recently been dredged at a considerable depth in West Indian waters. This family, with the last, possesses the striking anatomical feature of having the heart traversed by the digestive tract. It also has two gills, the degree of torsion in the visceral mass not being sufficient to have crowded out and destroyed the original right gill. The shell is spiral, but is so greatly flattened, and the body-whorl is so greatly extended, that the shell quite loses the spiral appearance. Along the dorsal side of the shell is a row of holes, through which project numerous tentacular processes from the mantle. The outer surface of the shell, before it is polished, is usually rough and unattractive, but within, when the [pg359] animal is removed, it displays a most beautiful and highly colored nacreous surface. The spot near the center of the inner shell surface where the muscles of the foot were attached is usually most brilliantly colored. The shell of the abalone is susceptible of taking a very high degree of polish, and is extensively used in commerce for colored mother-of-pearl and for inlaid work. Haliotis is a vegetable-feeding genus. They cling with great tenacity to rocks about low tide, and it requires skill to remove them without breaking the shell. There are several species in California. The Chinese use the abalone for food, and have waged a persistent war upon the family along the Pacific coast until the specimens are not nearly as common as formerly. They are also eaten in France and in Japan.
H. splendens. The largest and perhaps the most attractive in appearance of the Californian species. Speaking of this beautiful shell, Professor Keep says: "Within, a whole rainbow is condensed in one of the magnificent shells, though the shades of green are most conspicuous. The coloring in the center is particularly fine, resembling a peacock's tail. There are about six open holes near one side of the shell, and its length is about the same number of inches." (Plate LXVI.)
H. rufescens. A large abalone, which sometimes attains a length of eight or nine inches. It is red in color, with three open holes in the body-whorl. The outer portion of the shell is usually incrusted with mineral deposit and overgrown with vegetation.
H. cracherodii. Very dark green without, with five to nine holes; length from one to six inches; spire exceedingly short. Common on the Californian coast in crevices of rocks at low tide.
Family TROCHIDÆ
This is one of the largest and most interesting families of the Mollusca. It contains many apparently widely separated genera and a host of species, which for the most part are littoral, the majority actually living between tide-marks. The typical trochid shell is top-shaped or pyramidal, having a broad base and many closely wound flat whorls terminating in a sharp apex. All the trochids are nacreous within the aperture—a character which is constant throughout the family. The animal has but one gill (the left), a short snout, and often frontal lobes on the head. The edge of the mantle or the epipodial line of the foot is usually ornamented with from three to five cirri. The tentacles are [pg360] long and slender, with short peduncles for the eyes; the operculum is corneous, with a central nucleus. The animals are herbivorous, feeding upon algæ. The trochids are essentially tropical shells, and the most of the genera which are comprised in the family are only to be encountered in the warm waters of the Pacific and Indian oceans. Some forms are very beautiful, and frequently are used as mantel ornaments, and the shells of one little species, which is opalescent in its coloring, are still extensively gathered in the East Indies, to be polished and strung like pearls in necklaces.
Genus Margarita
On the Atlantic coast north of Cape Cod the trochids are represented by the genus Margarita, with five or six species. The shells are small, thin, and globosely depressed, with smooth or transversely striated whorls. The aperture is nearly circular, with a simple lip.
M. cinerea. This species has several prominent revolving ridges upon the upper side of the whorls, with finer ones on the base. Very fine growth-lines cover the entire shell. It ranges all along the coast north of Cape Cod, but is not usually found between tides. The writer has dredged many specimens in shallow water at Eastport and Bar Harbor.
M. helicina. A thinner and more globose species than the last, with a translucent, shining, smooth surface of a yellowish or olive color. M. helicina is very fond of the leaves of Laminaria, and is often found clinging to them when storms have torn these great algæ from the bottom and cast them upon the shore. At Bar Harbor they are common upon the eel-grass in Rodicks Weir. This species can generally be distinguished by its iridescent, metallic luster.
M. undulata. A commoner species, perhaps, than either of the preceding, sometimes found on the rocks of sheltered coves at exceptionally low tides. Judging from the number often to be found in the stomachs of fishes, they must be considered excellent food by the cod and its allied species which thrive along the Maine coast. No doubt millions of M. undulata are yearly destroyed in this way. The shell is depressed, with four rounded whorls, a flattish base, and a large umbilical opening. In color it varies from rose-red to brown. The surface is decorated with numerous revolving raised lines placed at uniform distances. Just below the suture the body-whorl is somewhat undulated with short folds. Height three tenths of an inch, base four tenths of an inch. [pg361]
Genus Calliostoma
This genus is better represented on the Pacific coast of the United States than upon the Atlantic. It comprises a series of marvelously beautiful shells, often exquisitely colored. They are regularly conical or pyramidal in shape, with flattened bases. One never tires in the search for calliostomas. They are not common enough to cause one to lose interest, and whenever a good specimen is captured it seems as though one had found some gem cut and polished by nature's skilful hand and prepared for a place of honor in the cabinet.
C. occidentale. The only species of this genus found on the northeast coast. It is larger than Margarita cinerea, but somewhat resembles it. It is shining nacreous within and without, and has strong revolving ribs, the upper one on each whorl often being broken into a circular row of white dots. The lip is crenulated. This very pretty species is not likely to be met with upon the shore, but may be dredged in shallow water on gravelly bottoms along the Maine coast. Height about one half of an inch.
C. jujubinum. A species which occurs in the waters of Florida. Its form is almost that of a true pyramid. The sutures can scarcely be distinguished. The shell is marked by brown and purplish-red spots on a white background, and has numerous revolving ribs broken into rows of white dots like little glazed beads. The umbilicus is funnel-shaped and wide. In Tampa Bay this shell is frequently found on sponges, and may sometimes be gathered on the beach after storms, even as far north as Hatteras. There are as many as twenty species of this genus in American Atlantic waters, but they are either rare or have deep-water stations.
C. annulatum. A remarkable species of Calliostoma, found in California. The whorls are adorned with revolving rows of raised dots, and the sutures are frescoed in exquisite purple. This beautiful species lives upon seaweed, and on pleasant days comes to the surface of the water. It can then be collected from a boat by drawing in quantities of seaweed. It is very unlikely that the collector will ever find a specimen upon the beach, for the shell is too fragile to withstand the rough handling of the waves. Length one inch.
C. canaliculatum. The largest member of this genus to be found in American waters. It resembles the last species in form, but lacks the purple sutures. The revolving ribs are very numerous and prominent. There is no umbilicus. Length one to one and a half inches. Found on the Pacific coast.
C. costatum. A heavier shell than the preceding, with somewhat more rounded whorls. Reddish-brown in color; numerous revolving ridges; no umbilicus; about three quarters of an inch in length. It is found in rocky places, and sometimes in considerable numbers, just at low-tide mark. Found in California. [pg362]
Genus Chlorostoma
This genus is represented in California by several species, the commonest of which is probably C. funebrale—a doleful name, no doubt given on account of the jet-black color.
C. funebrale. The shell is thick and strong, like most between-tide species, which are constantly exposed to the buffeting of the waves. It is to be found in countless thousands upon rocks exposed at low tide, and may be gathered at any time except full flood-tide, like the littorinas and purpuras of the east coast. Within the aperture the surface is nacreous and greenish in tint; the last whorl is drawn in, like gathers, at the suture. The umbilicus is closed. There is a white nodule at the base of the lip of the columella. Length one half of an inch to one inch. (Plate LXVII.)
C. brunneum. This species is brown, as its name would indicate, and there is greenish nacre within the aperture. It lives upon kelp, or upon rocks at very low tide. Length about an inch. (Plate LXVI.)
Genus Trochiscus
T. norrisi. A flattened shell with rounded, dome-like spire and obtuse apex; a fairly common species. It has a wide, deep umbilicus and a sharp lip. It is of a rich brown color, with dark chestnut about the umbilical region and greenish-white within the umbilicus; there is a band of dark olive-green about the inner margin of the lip. The shell is about two inches in diameter and of a somewhat greater height. The operculum is multispiral, with a central nucleus, and is shaggy and rough. Like all other trochids, it feeds upon algæ. It is often found upon the beach after violent storms. Found in California, south of San Francisco. (Plate LXVI.)
Genus Livona
L. pica. This large and interesting trochid is a West Indian species which sometimes occurs in Florida. It lives about coral reefs and rocky shores, attaching itself in vast numbers to the rocks. This shell is a favorite refuge for large hermit-crabs. It is a curious sight in certain of the West India islands to see a Livona pica shell scrambling up a tree, looking very much out of place upon the back of some terrestrially inclined crustacean. When well cleaned it is a beautiful shell, with black wavy lines over a greenish-white nacreous foundation. The animal has a row of waving cirri upon each side of the mantle, and long, slender tentacles. It is largely used as an article of diet in the West Indies and Central America. (Plate LXVII.)
Family TURBINIDÆ
This family is very closely allied to the trochids, the most striking difference being in the operculum, which in the Turbinidæ is calcareous and usually smooth and very convex on the outside. [pg363] The shells are nacreous within, and the animal, with its rows of waving cirri upon each side, is very suggestive of Trochus. They are, for the most part, shallow-water or littoral forms.
| PLATE LXVI. | |
|---|---|
| 1, Lucapina crenulata. | 3, Chlorostoma brunneum. |
| 2, Haliotis splendens. | 4, Neritina reclivata, enlarged. |
| 5, Trochiscus norrisi. | |
| PLATE LXVII. | |
|---|---|
| Livona pica, reduced. | Turbo castaneus, enlarged. |
| Nerita peleronta. | Chlorostoma funebrale. |
| Nerita tessellata. | |
Genus Turbo
T. castaneus. This species has a range as far north as Cape Hatteras, and is especially abundant at Tampa, on the west coast of Florida. The peculiar operculum is sufficient to identify the genus at once. One variety of this species has a crenulated shoulder upon the body-whorl and is referred to as Turbo crenulatus, A series of intermediate forms establishes the specific identity of the two varieties. (Plate LXVII.)
Family NERITIDÆ
The Neritidæ are strictly littoral forms, almost entirely confined to the warmer waters of tropical seas. The animal preserves the usual diatocardian features—has a short snout and long tentacles. Unlike the trochids and Turbo, it has no cirri along the epipodial margin. The shells are peculiarly shaped, the spire being greatly flattened and scarcely noticeable on account of the unduly large development of the body-whorl; thus the shell takes on a decidedly patelliform appearance. It is without an umbilicus. In the principal genus Nerita the outer lip is sharp on the edge, but greatly thickened just within.
Genus Nerita
N. peleronta. This shell has two teeth on the wide, flat columellar lip, and about them is a blotch of red, suggesting blood. The common name of this shell, "bleeding-tooth," is very appropriate. Found in southern Florida. (Plate LXVII.)
N. tessellata is a smaller species, with heavy revolving ribs, and is further decorated with transverse oblique black lines. The operculum is calcareous. Both of these species have the habit of absorbing the entire inner portion of their shells. They belong to the West Indian fauna, and occur in great numbers on rocky or coral shore stations. They also may be found on the east Florida coast, well to the south. A third species, N. versicolor, often occurs, associated with the other two. It is somewhat smaller than the others and can easily be distinguished by the four teeth on the columellar lip, the edge of the columella being convex. (Plate LXVII.)
Genus Neritina
The genus Neritina is very closely allied to the last, having quite the same form of shell; but it is usually more globular and [pg364] variously ornamented by bright spots or zigzag lines of coloration. The neritinas have acquired the habit of ascending rivers, until they have become almost wholly a brackish- or fresh-water genus. The metropolis of this genus is in the South Sea Islands, where it attains a wonderful development in the clear running streams of the volcanic islands.
N. reclivata. A very pretty olive-green species, with very fine, wavy, longitudinal lines of coloration, found in almost all Floridian streams above the action of the tide. The nacre of the columella and within the aperture is bluish-green, and the operculum is rich olive. (Plate LXVI.)
N. viridis. A small, intensely green species, which, unlike most neritinas, is strictly marine. It belongs to the great West Indian faunal province, but is occasionally found upon the shores of Florida and of Texas.
The prosobranch gasteropods thus far considered (belonging to the suborder Diatocardia) all show by their anatomical structure that the process of visceral torsion, though carried very far within them, has not been complete enough to crowd out and finally destroy one of each of the paired organs. Both auricles of the heart (with some exceptions) were left intact.
In this the second suborder of the prosobranch gasteropods, the twisting visceral process has been carried to the extreme. The heart has but one auricle. There is but one gill (on the left side), and this is attached to the inner side of the mantle flap. In other respects the presence of certain specialized organs would probably indicate that gasteropods belonging to this suborder are a step higher in the scale of life than those which belong to the Diatocardia.
Family JANTHINIDÆ
Genus Janthina
The genus Janthina has an exceedingly thin and semi-transparent shell, deep violet in color on the base and lighter blue on the spire. An interesting feature of this genus is the mode of depositing the ova. The female exudes from a gland in the foot a [pg365] glutinous secretion which hardens in water, and, being filled with air-bubbles, constitutes a float. On the under side of this are deposited the eggs in rows of little capsules. While attached to this float it is impossible for a Janthina to sink, and hence it is that so many of these creatures are sacrificed in onshore gales of wind.
J. fragilis. The shell of this species is so brittle and fragile that it is very clearly not adapted to a life near shore. It is in reality a pelagic species which is occasionally blown ashore during easterly gales along the Atlantic coast of the United States. Vast numbers of these pretty creatures are sometimes encountered far out at sea, floating quietly on the surface. When storms drive them upon the beach, they become utterly helpless; since their foot is not adapted for crawling upon the sand, they soon perish, and their brittle shells are demolished by the surf. In Florida the beaches are sometimes fairly lined with Janthina shells, which make a band of purple along the high-tide mark as far as the eye can reach; then it may be years before they again appear. (Plate LXVIII.)
Family SCALIDÆ
Genus Scala
The shells of Scala have such a peculiar scheme of decoration that once seen they can never be mistaken. They are generally pure white, with well-rounded whorls, all of which are crossed at even distances by greatly elevated and smooth ribs. Each rib represents a rest-period, when the creature thickened the rim of the shell-aperture. The aperture is generally round, with a continuous lip. The animal has a retractile proboscis and long, slender tentacles with eyes at the outer bases, and is a predaceous, [pg366] carnivorous creature. Some Asiatic species of this genus, remarkable for their beauty and rarity, have been greatly prized by collectors. A single specimen of the now well-known S. pretiosa of China has been sold for two hundred dollars—a fancy price, indeed, for a shell which can now be bought for a dollar! There are over fifty species of Scala on the Atlantic coast, but most of them are either rare or belong to a zone of deeper water; there are, however, four or five species which are exceedingly common.
S. lineata. A species which ranges from Hatteras to New England. It has about eight whorls, and is slightly brownish in color. The ribs are robust and not greatly elevated; there are from seventeen to nineteen on the body-whorl. The shell is sometimes painted with a few revolving brownish lines.
S. multistriata. The transverse ribs are much smaller but very numerous; the small spaces between them are marked with many fine revolving lines. Found from Cape Cod southward.
S. groenlandica. Essentially an arctic species, which has found its way down to the New England coast. It is readily distinguished by the flattened, coarsely rounded, revolving ribs, which follow the volutions of the spire. Over them are the usual transverse heavy ribs peculiar to this genus.
S. angulata. The whorls touch one another only by the ribs, of which there are nine to each volution. This species has a remarkably wide range, occurring from Cape Cod to southern Florida. (Plate LXVIII.)
These four species vary from one half of an inch to one inch in length. All of them are found on the beach after storms or may be dredged in shallow water near the shore.
Family NATICIDÆ
This large and interesting family is well represented in the Atlantic waters of the United States, but its more beautiful members live in the tropics. The New England and New Jersey species are dull in color, but offer much of interest to the collector and student. The foot is enormously large, and carries in front a great shield-like fleshy process, which curves back over the head of the animal and serves as a plow in pushing its way through the heavy wet sand of the beach. When the creature is thus seen extended in the act of crawling, one wonders how it is possible for it to withdraw so great an amount of body into its shell; but if it is suddenly seized or irritated, it will quickly [pg367] demonstrate its ability to hide itself completely within its house and to close the door very effectively by means of its operculum. The eyes seem to be wanting, or they are concealed under the skin of the head. The shell is usually quite large, with a depressed spire and well-rounded whorls—especially the body-whorl, which appears to be greatly swollen. The umbilicus is usually open and moderately large, the lip simple.
| PLATE LXVIII. | |
|---|---|
| Janthina fragilis. | Sigaretus perspectivus, upper side. |
| Scala angulata, enlarged. | Sigaretus perspectivus, under side. |
| Natica canrena. | Crepidula aculeata. |
Genus Polynices (Lunatia, Natica).
P. heros (generally referred to as Lunatia or Natica heros). One of the commonest large shells and one of the most characteristic species of the New England and New Jersey littoral fauna. It is exceedingly common along the Long Island shore, where it may be found on the open beach, in pools with a sandy bottom left by the receding tide. It is usually partially and frequently wholly buried in the sand. The umbilicus is open and large, the operculum corneous, and the shell heavy and ashy-white to brownish, with (when young) a yellowish epidermis. Its length is from two to four inches. It has no ornamentation whatever. P. heros is a most voracious creature and spends its time in hunting for flesh—either alive or dead—to devour. It feeds upon dead fish, or upon other mollusks whose shell it is able to pierce by means of its radula, making a little round hole through which it sucks out the flesh from within. The curious egg-cases of this species have already been referred to. (See Plate I.) It glues together particles of sand into the form of a basin with the bottom knocked out and broken on one side. In the gelatinous substance of this basin it deposits its eggs in a regular order. These hatch out in midsummer. Egg-cases of this kind can always be found wherever Polynices lives. For a long time naturalists were greatly puzzled by these curious things, and their blunders are recorded in earlier works, where these egg-cases have been elaborately described as living animals belonging to various invertebrate orders. The largest and best specimens of P. heros are to be found south of Cape Cod. (Page 343.)
P. triseriata. A small shell of exactly the same shape as P. heros, but decorated with three revolving series of bluish or chestnut spots. It is pretty well determined that this so-called species is only the young of P. heros. It is very abundant all along the coast.
P. duplicata. This is even more abundant than P. heros. It has a flatter shell, with an obtuse apex and dome-like spire. The umbilicus is partly or wholly closed by a thick, callous, shelly process thrown off from the columellar lip, and is chestnut in color. The surface of the shell is smooth, often polished, ashy-white below and light chestnut above. The operculum is corneous. The length of the shell varies in different localities from one half of an inch to about two [pg368] inches; the breadth slightly exceeds the length. P. duplicata has a very extensive range, from the Gulf of Mexico to Newfoundland. The largest and finest specimens are found in the vicinity of New York and at Hatteras. In Florida they are usually smaller. This species cannot be confounded with any other upon our coast on account of the heavy callous deposit over the umbilicus. Its habits are similar to those of P. heros.
Natica clausa. A Northern species which is fairly abundant on the Maine coast. It has a shelly operculum, and the umbilicus is neatly closed by a pure white, shining callosity. Its length is about one half an inch, its color livid white to light brown, white within. The calcareous operculum at once determines this shell. This species (as well as the following one) has retained the generic name of Natica because of the shelly operculum, as explained below.
N. canrena. One of the handsomer species of Natica, which occurs in Florida. Sometimes it is seen as far north as Hatteras. The shell is white, with bars of light chestnut circling the whorls, and with zigzag lines of darker purplish hue crossing them. The base of the shell is white. The aperture is large and flaring, and is purplish within. The umbilicus is partially closed by an entering callous plug. The operculum is calcareous, with eccentric, deeply cut grooves. Found in sandy stations just about low-water mark. (Plate LXVIII.)
P. lewisii. A species which occurs on the west coast of the United States. It resembles its New England relative P. heros very closely. P. lewisii is a Northern species, and does not range south of Oregon. Professor Keep mentions one specimen of the size of a six-inch globe, but such dimensions are very unusual. A good-sized specimen need not exceed four inches in height.
P. recluziana. A species well known on the southern coast of California. The umbilicus is closed by a thick, highly polished white callosity, and the general shape of the shell is strongly suggestive of the common east-coast species P. duplicata. A large specimen is about two inches in diameter.
[There has been much confusion in the generic nomenclature of this family. The old name Natica once did service for all the species; then the names Lunatia, Neverita, and Polynices were applied to certain special forms; but it has been wisely proposed by conchologists to use the name Natica for those forms having a shelly operculum, and to adopt the name Polynices for those having a corneous operculum. Lunatia and Neverita have become subgenera of Polynices.] [pg369]
Genus Sigaretus
A very interesting species of this genus occurs on the east coast, sparingly in New Jersey, but very abundantly south of Hatteras. Sigaretus is a modified Natica. The spire is flattened and minute. The body-whorl, being greatly expanded, gives a wide, flaring, oblique aperture. The shell is ear-shaped and white, with fine revolving lines. There is no umbilicus. The operculum is small and rudimentary. The animal is large, with an enormous foot and greatly developed propodium, and is a sand-dweller. The common east-coast form is S. perspectivus. (Plate LXVIII.)
Family CAPULIDÆ
Genus Crepidula
C. fornicata. All collectors of mollusks on the Atlantic coast sooner or later encounter this exceedingly common species adhering to oyster-shells or scallops, and often to other large live shells. It is cast upon the beach along the entire length of the Atlantic coast. The shell is obliquely oval, dull whitish in color, and either smooth or rough or even ribbed, according to the nature of the surface to which it clings. The spire is almost entirely suppressed, the little inconspicuous apex being turned to one side and closely pressed down against the body of the shell. When looking into the interior of the shell one is reminded of a boat, for the upper portion of the aperture is covered by a horizontal shelly partition, called the diaphragm, a space being left below which would correspond to the forecastle of a ship. The "stern" is round, and the "bow" is suggestively pointed.
C. plana. In this species the shell is white and flat, or slightly concave. Although it is pointed at the "bow" end and square at the "stern," the nautical resemblance stops there, because, being flat, there are no swelling sides and bow. The diaphragm is about one half the length of the shell, convex, shining, white, and translucent. C. plana lives generally within the aperture of large dead shells. It has a wide range, from Maine to Florida.
C. aculeata. A common Floridian species which has a remarkable range, being found in nearly all the tropical and semi-tropical waters of the world. It is smaller than C. fornicata, is reddish-brown with a white diaphragm, and has several radiating ribs on the back, which are inclined to be nodulous. (Plate LXVIII.) [pg370]
On the Pacific coast the following species are found: C. adunca, with a strongly recurved apex, and less than one inch long; C. rugosa, rough, brown, with the apex lying on the edge of the shell, and one inch in length; C. navicelloides, almost identical with the east-coast C. plana. C. aculeata also appears.
Genus Crucibulum
Crucibulum has a peculiar rounded shield-like form, with a very small apex on one side. Within there is a cup-shaped appendage attached by one side to the inner margin of the shell. This latter feature at once determines the genus.
C. striatum. This species has radiating riblets, cut by circular lines of growth. No dimension would quite reach an inch. It is a common shell on the Atlantic coast, and will be found adhering to stones and other shells, but it is not, strictly speaking, a littoral species.
C. spinosum. The shell exhibits a strong tendency to spinous processes on its back. Found along the southern part of the California shore.
Family LITTORINIDÆ
Genus Littorina
Littorina is probably the most characteristic genus of Northern littoral regions. Together with some of its allied genera it is also, probably, equally characteristic of various tropical littoral faunas all over the world. The family comprises strictly between-the-tides genera and species. Indeed, it is suspected that some species of Littorina are making very fair progress toward a terrestrial condition, for they actually live above high-tide mark,—even in the branches of overhanging trees,—and must certainly pass days at a time out of their natural element. That such a transformation is possible need not for a moment be doubted, for there are many land mollusks to-day that give abundant evidence of having been at some past time aquatic or marine species. These changes in nature are constantly going on, and the gradual substitution of a lung for a gill is no very startling metamorphosis. [pg371]
The littorinas fairly swarm in favorable localities upon all shore stations. In Maine and Massachusetts the bold, rocky coast furnishes a home for several species. Often the rocks at low tide are black with them; the algæ that cling in wet masses to the exposed rocks are alive with them. One cannot walk about in such localities without crushing hundreds of specimens. Sometimes they will be found clinging in clusters upon the piling of old wharves, or crawling about the bottom at or about the low-tide mark. The best specimens of Littorina are found in stations where they are bathed twice a day by pure, uncontaminated sea-water; those living near the mouths of streams, or where the water is brackish or impure, are usually small and degenerate. They are vegetable feeders, and have received the common name of "periwinkles." In Great Britain they are used among the poorer classes for food. The animal has a short, broad muzzle, and eyes at the outer bases of the tentacles. The foot is longitudinally grooved, and there is a rudimentary siphonal fold in the mantle. The shells are turbinated, usually heavy, few-whorled, and with a round aperture.