C. ventricosa is considered by some authors to be equivalent to C. affinis var. semicircularis Lagerst., Encyonema prostratum (Berk.) Ralfs, E. cæspitosum Kuetz. and E. auerswaldii Rab. H. L. Smith's Type Slide of C. ventricosa Ag. is said to equal C. affinis Kuetz., but the specimens appear to me to be equivalent to C. ventricosa Kuetz. Cleve unites many forms, including E. cæspitosum, under C. ventricosa.
CYMBELLA PROSTRATA (BERK.) CL.
Valve semi-elliptical, obtuse at the apices, which are sometimes prolonged and turned downwards; median line straight, terminal nodules distant from the ends; axial area narrow, central area rounded; striæ in radiating, slightly curved lines, indistinctly punctate.
Common in fresh water; occasional in brackish.
Pl. 18, Fig. 21 (represents a frequent variation).
CYMBELLA PHILADELPHICA N. SP.
Valve semi-elliptical-lanceolate, with rounded apices; ventral margin strongly gibbous; terminal nodules distant from the ends; axial area broad, central area widened on the dorsal side; striæ radiate, not curved nor of unequal length, indistinctly punctate, 10 in 10 µ on the dorsal, 8 in 10 µ on the ventral side. L. 86 µ.
This form approaches Encyonema prostratum (Berk.) Ralfs, Schmidt's Atlas, Pl. 71, Fig. 7, but differs in the striæ and the axial and central areas.
Blue clay of Philadelphia. Rare.
Pl. 18, Fig. 8.
CYMBELLA TRIANGULUM (EHR.) CL.
Valve semi-elliptical, with acute ends; median line straight; ventral side half the width of the dorsal, with straight, slightly convex or concave margin; striæ radiate, coarsely punctate.
Glœonema triangulum Ehr.
Baker's Run, Willistown, Pa.
Pl. 18, Fig. 24.
CYMBELLA TURGIDA (GREG.) CL.
Valve semi-elliptical, with acute ends; ventral margin gibbous; ventral side half the width of the dorsal; median line straight; terminal fissures turned downwards; axial area broad; striæ radiate, coarsely punctate.
Baker's Run, Willistown, Pa.
Pl. 18, Fig. 23.
CYMBELLA TURGIDA (GREG.) CL. VAR. ?
Valve lunate, with gibbous ventral margin; median line straight; terminal fissures turned downwards near the ends; axial area lanceolate, striæ radiate on the dorsal side, 8 in 10 µ, punctate, 9 on the ventral side, closer at the ends where they are convergent. L. 65 µ. Not a typical form.
Willistown, Pa.
Pl. 18, Fig. 12.
CYMBELLA RHOMBOIDEA N. SP.
Valve rhomboidal, with acute ends; dorsal part one and a half times the width of the ventral; median line nearly straight, with terminal fissures turned downwards near the ends; axial area broad, not widened in the middle, except slightly on the ventral side; striæ radiate, distant in the middle of the dorsal side where they are 7 in 10 µ, coarsely punctate, the puncta in longitudinal lines, 9 in 10 µ on the ventral side, closer at the ends. L. 69 µ.
Baker's Run, Willistown, Pa.
Pl. 18, Fig. 11.
CYMBELLA GRACILIS (RAB.) CL.
Valve semi-lanceolate, with acute ends; median line nearly straight, with terminal fissures turned downwards, distant from the ends; axial area linear; ventral margin straight or slightly gibbous in the middle.
Hammonton Pond, N. J.
Pl. 18, Fig. 20.
CYMBELLA LACUSTRIS (AG.) CL.
Valve elliptical-lanceolate, with obtuse ends, nearly symmetrical; median line straight, terminal fissures distant from the ends; striæ radiate in the middle, convergent at the ends, coarsely lineate.
Belmar, N. J.
Pl. 18, Fig. 25.
(amphora, a jar)
Valves asymmetrical along the longitudinal axis, as in Cymbella, but with the plane passing through the dorsal and ventral sides of one valve at an angle with that of the other. As Cleve states, Cymbella and Amphora are forms of Navicula "with both valves similar and asymmetrical along the longitudinal axis," and the difference between Cymbella and Amphora is in the "degree of asymmetry." If, following H. L. Smith's diagrams (Lens, Vol. 2, 1873, p. 66), we assume that the usual form of the valve in Navicula is elliptical or lanceolate, and the zone view is rectangular, we have in Cymbella an arcuate median line and a more or less reniform valve, while the zone view remains rectangular with the valves parallel. Now, if the valves are asymmetrical along the longitudinal axis, and one side of one valve is separated from the corresponding side of the opposite valve by a wider connective zone than is the case on the other side, the transverse section of the frustule will appear cuneate, as in Amphora, and the connective zone will be wider on one side than the other. When, therefore, we examine an entire frustule as it is usually seen, we shall find the two raphes of the valves in focus at the same time on the ventral side, and, by changing the focus, the convex sides of the same valves are seen, the dorsal view with, usually, a wider connective zone. As an illustration, compare Figs. 5 and 6, on Plate 15, Fig. 6 being the ventral, and Fig. 5 the dorsal view.
As Amphoræ are epiphytic or parasitic, they are considered, as Cleve remarks, like Achnanthes and Cocconeis, as "degenerated forms."
Chromatophores usually single, lying on the ventral connective zone. Mereschkowsky describes nine forms.
Cleve divides the genus into a number of groups as follows:
Amphora proper.—Connective zone not complex; valves with longitudinal lines on the dorsal side; coarsely punctate or costate.
Diplamphora.—Zone complex; otherwise as in Amphora.
Halamphora.—Longitudinal lines absent; frustule elongate, with protracted ends.
Oxyamphora.—Zone complex; longitudinal lines absent; frustule elliptical; valve lunate, with or without a central stauros; striæ punctate.
Amblyamphora.—Zone complex; frustule rectangular; valve lunate; striæ punctate; axial and central areas indistinct.
Psammamphora.—Zone not complex; frustule rectangular; central nodule frequently dilated to a stauros; no axial or central area.
Cymbamphora.—Valve semi-lanceolate; median line straight, approximate to the ventral margin.
Amphora
AMPHORA ROBUSTA GREG.
Frustule elliptical, truncate; valve lunate, with straight ventral margin; median line biarcuate; ventral side with coarse, radiate striæ, 6 in 10 µ, on both sides of the median line.
Along the coast.
Pl. 15, Fig. 1.
AMPHORA PROTEUS GREG.
Frustule elliptical, truncate; valve lunate, with straight ventral margin; median line biarcuate; no central area. Striæ on the dorsal side not interrupted, 9 in 10 µ. Ventral side striate toward the ends.
Differs from A. robusta chiefly in size and coarseness of puncta. Extremely variable in size.
Common along the coast.
Pl. 15, Figs. 5, 6, and 19.
AMPHORA OVALIS (BRÉB.) KUETZ.
Frustule elliptical, truncate; valve lunate; median line biarcuate; striæ on dorsal side 10-16 in 10 µ.
Var. libyca (Ehr.) Cl.—Central area distinct on the dorsal side.
Var. pediculus (Kuetz.) Cl.—Central area and nodule quite distinct. Striæ finer than in var. libyca.
Common in ponds. Quite variable.
Pl. 15, Fig. 7.
AMPHORA GIGANTEA VAR. FUSCA A. S.
Frustule elliptical; valve lunate, with straight ventral margin. Axial area absent on the dorsal side; dorsal striæ, 10 in 10 µ, punctate. Ventral part hyaline except at the ends, which are obliquely striated, with short, punctate lines. L. 70-120 µ.
Absecon, N. J.
Pl. 38, Fig. 1.
Diplamphora
AMPHORA CRASSA GREG.
Valve linear-elliptical, with obtuse, incurved ends. Median line biarcuate. Axial and central areas indistinct on the dorsal side; striæ coarsely punctate, interrupted by a longitudinal line on the dorsal side.
Along the coast.
Pl. 15, Fig. 3.
AMPHORA AREOLATA GRUN.
Valve with straight ventral margin; median line straight, approximate to the ventral margin; axial area indistinct; several longitudinal lines crossed by apparent costæ which alternate with rows of fine puncta.
Blue clay. Rare.
Pl. 15, Fig. 11.
Halamphora
AMPHORA COFFÆIFORMIS (AG.) KUETZ.
Frustule lanceolate, truncate; zone with numerous divisions. Valve arcuate on the dorsal and nearly straight on the ventral side; ends protracted or slightly capitate.
A. aponina Kuetz.
A. salina Wm. Sm.
Along the coast.
Pl. 15, Figs. 8 and 18.
Oxyamphora
AMPHORA LINEOLATA EHR.
Frustule membranaceous, elliptical, truncate, with broad ends. Zone with numerous divisions. Dorsal part striated transversely; ventral side with longitudinal lines.
A. plicata Greg.
A. hyalina H. L. Smith, Type No. 64.
Along the coast.
Pl. 15, Figs. 9 and 10.
AMPHORA OSTREARIA BRÉB.
Frustule oblong, with rounded angles. Zone with five or more divisions transversely striated. Central area narrow, biarcuate; central nodule dilated to a stauros. Valve narrow, with arcuate dorsal and straight ventral margin, acute at the ends. Striæ transverse, finely punctate.
A. vitræa Cl.; A. porcellus Kitton; A. quadrata Bréb.; A. elegans Greg. Appearance varies according to the position of the valve.
Along the coast.
Pl. 15, Figs. 12 and 21.
AMPHORA LÆVIS GREG.
Frustule oblong, hyaline and membranaceous. Valve linear or slightly arcuate, with ventral margin tumid in the middle; ends obtuse; central nodule dilated to a stauros; median line very narrow, biarcuate, coinciding with the dorsal margin at the ends; striæ transverse, punctate.
Blue clay.
Pl. 15, Fig. 13.
AMPHORA ACUTA GREG.
Valve lunate, with acute ends; ventral margin straight; ventral side very narrow. Central nodule dilated to a stauros; striæ transverse, punctate.
Along the coast.
Pl. 15, Fig. 20.
Amblyamphora
AMPHORA OBTUSA GREG.
Frustule rectangular. Valve linear, obliquely rounded at the ends, with arcuate dorsal, and straight ventral, margin; median line biarcuate; striæ, 18-20 in 10 µ.
Along the coast. Common.
Pl. 15, Fig. 4.
Psammamphora
AMPHORA ARENARIA DONK.
Frustule hyaline, rectangular, slightly tumid in the middle, with rounded angles. Valve linear with broad ventral side and straight or sinuate ventral margin. Striæ, 24-27 in 10 µ (Cleve).
Common along the coast.
Pl. 15, Fig. 17.
The distinction between A. obtusa and A. arenaria is not always evident if the valves alone are seen. The former has a complex zone, the latter a simple zone, and the valve has finer striæ. Cleve's descriptions and references in regard to these two forms do not agree with the descriptions and figures of H. L. Smith, or with the figures of Schmidt. The valves of most Amphoræ are capable of assuming various outlines according to their position.
AMPHORA OCELLATA VAR. CINGULATA CLEVE
Frustule rectangular. Valve linear, with dorsal margin arcuate and the ventral margin straight. Central nodule with a stauros on the dorsal side.
Squan River, N. J.
Pl. 15, Figs. 14 and 15.
Cymbamphora
AMPHORA ANGUSTA VAR. EULENSTEINII GRUN.
Valve lanceolate, acute at the ends. Median line straight, approximate to the margin. Axial area widened on the dorsal side, indistinct on the ventral; striæ punctate.
A. eulensteinii A. S.
Common along the coast.
Pl. 15, Fig. 16.
On Pl. 40, Figs. 21, 22, and 23, I have attempted, imitating H. L. Smith's figures (Lens, l.c.), to illustrate the difference in the transverse sections of Navicula, Cymbella and Amphora.
Fig. 21 represents the transverse section of a convex Navicula, in which the valves ecg and fdh are parallel, and the median nodules c and d are central.
Fig. 22 is a transverse section of Cymbella in which the valves are nearly parallel and the median nodules are excentric. The girdles on one side, ea and af, are narrower than gb and bh on the other side.
Fig. 23 is a transverse section of an Amphora in which the valves appear in zone view with the median nodules of both valves on the same side. The girdles on the ventral side, ea and af, are narrower than gb and bh on the dorsal side. The girdles on the dorsal side are seldom as broad as gb and bh, the valve extending over a great part of the dorsal side to g′ and h′.
(amphi, on both ends, and prora, a prow)
Frustule twisted in the longitudinal axis, constricted in the middle; zone complex, with numerous divisions crossed by fine striæ. Valve lanceolate, acute. The raphe confined within a sigmoid keel or extension of the valve; the central and terminal nodules indistinct. Striæ transverse, punctate, with coarser striæ at the junction of the keel and lower part of the valve.
Chromatophores single, with indented border except in A. pulchra, in which there are two chromatophores with entire borders.
AMPHIPRORA ALATA KUETZ.
Frustule with a row of puncta at the junction line. Valve linear, acute at the ends. Median line sigmoid. Striæ lineate on the lower part of the valve, punctate on the keel.
Along the coast. Not common.
Pl. 14, Fig. 3.
AMPHIPRORA PULCHRA BAIL.
Frustule with sigmoid connective zone. Valve very convex, with sinuate keel and junction lines evident. In zone view and in valve view, one half of the frustule, owing to the elevation of the keel, is wider than the other half. Striæ punctate, coarser on the keel.
Not uncommon along the coast.
Pl. 14, Figs. 1 and 2.
AMPHIPRORA CONSPICUA GREV.
Valve linear or elliptical, with acute ends. Median line sigmoid, but the junction lines not evident. Striæ lineate, with coarser lines near the middle.
Not common. Port Penn, Delaware River.
Pl. 14, Fig. 4.
AMPHIPRORA ORNATA BAIL.
Frustule membranaceous, constricted in the middle, with well-marked folds extending from the junction line in both directions. Valve lanceolate, constricted in the middle and with protracted ends. Keel undulate on the edge.
A beautiful, transparent and delicate form, the only fresh-water species in our locality.
Delaware Water Gap, Pa.
Pl. 14, Figs. 6 and 7.
AMPHIPRORA PALUDOSA WM. SM.
Frustule membranaceous, constricted, with truncate ends. Valve linear, with acute ends. Striæ scarcely visible.
Cape May (Cleve).
Pl. 14, Fig. 5.
(tropis, a keel)
Frustule oblong, constricted in the middle; keel not sigmoid. Axial area not evident. Striæ very fine, punctate, in longitudinal lines.
TROPIDONEIS LEPIDOPTERA (GREG.) CLEVE
Valve with straight, median excentric line. Keel unilateral, projecting above the median line in zone view; central area small. Transverse striæ finely punctate. As usually seen, the valve is inclined. According to Karsten there are two chromatophores on the connective zone, each divided into four parts, each of which contains a large oval pyrenoid.
Amphiprora lepidoptera Greg.
Along the coast.
Pl. 14, Figs. 8 and 9.
(auricula, the ear, the shape of the valve)
Frustule globose. Valve reniform or cymbiform, elevated into a keel which is not sigmoid. Median line biarcuate. Differs from Amphiprora in not having a sigmoid keel.
AURICULA MUCRONATA (H. L. SMITH) PERAGALLO
In zone view, the median line deeply bisects the longitudinal axis, ending in a mucronate central nodule. Connective zone complex. Valve very complex, with ventral margin nearly straight and raphe excentric. Central nodule near the margin, terminal nodules small. Striæ, 35-40 in 10 µ (Cleve). Chromatophore single, on the ventral part.
Amphora mucronata H. L. Smith.
Amphora (?) insecta Grun.
Auricula insecta (Grun.) Cleve.
"A rare and very curious pelagic species" (Peragallo, Diat. Villefranche).
Prof. H. L. Smith included this form in his first century of "Species Typicæ Diatomacearum," which was issued prior to 1876, the date of publication, in Schmidt's Atlas, of Amphora insecta Grun.
Atlantic City, N. J. Rare.
Pl. 15, Fig. 2.
(scolios, twisted, and tropis, a keel)
Frustule linear, oblong. Median line sigmoid near the ends. Valve with transverse costæ alternating with two intermediate rows of puncta in oblique lines.
SCOLIOTROPIS LATESTRIATA VAR. AMPHORA CLEVE
Valve asymmetrical, with the median line curved. Frustule sub-acute at the ends. Median lines not on the same side of each valve of the frustule.
Abundant at Cape May, N. J. Not common elsewhere.
Pl. 14, Figs. 10 and 11.
(gomphos, a peg, and neis (naus))
Valve elongated, asymmetrical to the transverse axis; axial area narrow; central area rounded, stigmatic; striæ radiating, costæ alternating with double rows of fine puncta. An indistinct, longitudinal line near the border.
Chromatophores and conjugation have not been determined.
GOMPHONEIS HERCULANEUM (EHR.) CL.
Valve clavate, with rounded apex; costæ, 13 in 10 µ, alternating with double rows of fine puncta, 22 in 10 µ, in oblique rows; axial area narrow, central area rounded, with one stigma.
Gomphonema capitatum Ehr var. herculaneum Ehr., H. L. S., Type Slide No. 177.
Common in the blue clay.
Pl. 19, Fig. 2.
Pl. 38, Fig. 15, zone view of young frustule.
GOMPHONEIS MAMILLA (EHR.) CL.
Valve lanceolate, with rounded apex and base; striæ costate, 10 in 10 µ, alternating with double rows of fine puncta; axial area linear, sometimes oblique, central area small, with one or more stigmas.
Blue clay. Rare.
Pl. 19, Fig. 1.
In one frustule I noticed one valve with one stigma and the other with four stigmas.
The difference between G. mamilla and G. elegans is not very great. In the latter the central area is larger and the longitudinal lines not so near to the margin. The stigmas form a circlet. There appears to be a coincidence in the relation of Gomphoneis to Gomphonema, and that of the true Achnanthes to the group described by Cleve under Achnanthidium. In Gomphoneis and Achnanthes the striation is both costate and punctate while in Gomphonema and Achnanthidium the striation is punctate only.
(gomphos, a peg, and nema, a filament)
Valve elongated, asymmetrical with respect to the transverse axis; striæ transverse, usually radiate, punctate.
Chromatophore band single, the middle lying on one zone.
In conjugation, according to Thwaites and Pfitzer, from two mother cells, which do not form a positive union, two auxospores are developed parallel to the original frustules. In Plate 19, Fig. 19, I have drawn a representation of the auxospore formation as I have frequently observed it in a gathering sent me by Mr. T. C. Palmer, containing G. angustatum, a common species in this locality. The sagittal plane of the valve of the auxospore is at right angles to the plane of the valve of the mother cell. Two valves of one of the mother cells are seen separated, one on each side of the auxospore which is nearly twice the length of the original frustules. The two valves of the other mother cell are not shown as they are not usually found closely united. In the figure one valve alone of the auxospore is seen, the opposite valve not being in focus. The valves of the auxospore are usually more or less arcuate, as in Cymbella, to which the genus is closely allied.
Grunow divides Gomphonema into two groups, Asymmetricæ and Symmetricæ, according to the presence or absence of stigmas. Cleve suggests Stigmaticæ and Astigmaticæ as more suitable in order to agree with the Cymbellæ. The Stigmaticæ are found chiefly in fresh water, sometimes in brackish. All of the marine forms belong to the Astigmaticæ, which, however, include some common fresh-water forms. Many species of Gomphonema are stipitate, some occur in gelatinous masses, and others are free.
GOMPHONEMA MONTANUM SCHUM.
Valve slightly biconstricted, with obtuse apex and basis, somewhat cuneate; axial area linear, widened in the middle unilaterally; stigma, one; striæ about 11 in 10 µ, more distant in the middle, punctate.
Gomphonema subclavatum var. montana (Schum.) Cl.
Pavonia, N. J., artesian well. Rare.
Pl. 19, Fig. 3.
GOMPHONEMA GEMINATUM LYNG.
Valve biconstricted, with large, rounded, sub-truncate apex and broad, sub-truncate basis; striæ, 9 in 10 µ, radiate in the middle, alternately longer and shorter, transverse at the basis and near the apex where they again radiate, coarsely punctate, puncta, 12 in 10 µ. Axial area linear; central area rounded, with several large stigmas in a longitudinal row; terminal fissures hook-shaped.
Blue clay.
Pl. 19, Fig. 4.
GOMPHONEMA LANCEOLATUM VAR. INSIGNIS (GREG.) CL.
Valve lanceolate; axial area narrow; central area unilateral with one stigma; striæ with coarse and distant puncta.
Common and variable.
Gomphonema insigne Greg.
Pl. 19, Figs. 6 and 12.
Fig. 12 shows a unilateral central area. Fig. 6 is more clavate in outline with small central area. In both forms the coarse puncta are in distinct longitudinal lines in the middle.
GOMPHONEMA ACUMINATUM VAR. TURRIS (EHR.) CL.?
Valve clavate, with cuneate, acute apex; axial area distinct; central area unilateral with one stigma.
Blue clay.
Pl. 19, Fig. 11.
GOMPHONEMA ACUMINATUM VAR. TURRIS (EHR.) CL.
Valve clavate, with cuneate apiculate apex and narrow basis; axial area narrow, with a unilateral central space; stigma opposite the short striæ; striæ more radiate in the upper part, distant in the middle.
Smith's Island, Delaware River.
Pl. 19, Fig. 5.
GOMPHONEMA ACUMINATUM VAR. CORONATA (EHR.) CL.
Valve twice constricted, with broad, cuneate apex; striæ radiate in the middle, convergent near the apex and radiate at the apex. Variable in size and outline.
Blue clay. Fresh water. Common.
Pl. 19, Fig. 7.
GOMPHONEMA ACUMINATUM VAR. TRIGONOCEPHALA (EHR.) CL.
Valve broad, with cuneate apex; axial area narrow; central area unilateral with one stigma.
Pavonia, N. J., artesian well.
Pl. 19, Fig. 20.
GOMPHONEMA CONSTRICTUM EHR.
Valve clavate, constricted beneath the abruptly rounded apex, gibbous in the middle, striæ alternately longer and shorter; axial area narrow, central area unilateral, with one stigma.
Common in fresh water.
Pl. 19, Fig. 8.
GOMPHONEMA SPHÆROPHORUM EHR.
Valve clavate, with capitate or rostrate-capitate apex and narrow basis; axial area very narrow; central area small, unilateral, with one stigma.
Common in fresh water.
Pl. 19, Figs. 9 and 10. Fig. 10 appears to be a transitional form having a more distinct axial area and rostrate apex.
GOMPHONEMA AUGUR EHR.
Valve broadly clavate, truncate and apiculate at the apex; basis sub-acute; axial area distinct; central area small, unilateral with one stigma; striæ with distant puncta.
Blue clay. Willistown, Pa.
Pl. 19, Fig. 21.
GOMPHONEMA INTRICATUM KUETZ.
Valve narrow, lanceolate, slightly gibbous in the middle; axial area distinct; central area transverse with one stigma; striæ parallel. Quite variable.
Common in fresh water.
Pl. 19, Fig. 14.
GOMPHONEMA ANGUSTATUM KUETZ.
Valve lanceolate, with sub-rostrate apex and basis; axial area indistinct; central area unilateral, with one small stigma; striæ slightly radiate, indistinctly punctate.
Very common in fresh water.
Pl. 19, Figs. 18 and 19.
Fig. 19, as stated above, represents the formation of an auxospore.
GOMPHONEMA ÆQUALE GREG.
Valve linear-lanceolate, nearly symmetrical, with capitate apex and basis; axial area narrow; central area unilateral, with one stigma; striæ radiate in the middle, slightly convergent at the ends.
Gomphonema intricatum var. æquale (Greg.) Cl.
Blue clay. Not common.
Pl. 19, Fig. 15.
GOMPHONEMA SARCOPHAGUS GREG.
Valve linear, irregular in outline, with rounded apex and basis; axial area distinct; central area small, unilateral, with one stigma; striæ irregular with coarse, distinct puncta.
Occasional in fresh water.
Pl. 19, Fig. 16.
GOMPHONEMA CAPITATUM EHR.
Valve clavate, broad at the sub-truncate apex and slightly constricted, or with parallel margins; axial area linear, central area stellate, with one stigma; striæ in the middle alternately longer and shorter.
Blue clay.
Pl. 19, Fig. 22.
GOMPHONEMA PARVULUM VAR. MICROPUS (KUETZ.) CL.
Valve clavate, with rounded apex and basis; axial area indistinct; central area unilateral, with a small stigma; striæ distant in the middle.
Common.
Pl. 19, Fig. 17.
GOMPHONEMA VENTRICOSUM GREG.
Valve clavate, with broad apex and produced, rounded basis; axial area narrow, widened in the middle; stigma one; striæ distant in the middle, finely punctate.
Blue clay.
Pl. 19, Fig. 13.
GOMPHONEMA OLIVACEUM LYNG.
Valve clavate, with broad apex and narrow basis; axial area very narrow; central area irregular, without stigma; striæ radiate, finely punctate.
Very common.
Pl. 19, Fig. 23.
GOMPHONEMA BRASILIENSE VAR. DEMERARÆ GRUN.?
Valve lanceolate, with sub-cuneate apex and narrowed basis; axial area lanceolate, broad; no stigma; median fissures remote; striæ parallel, 12 in 10 µ, punctate, the puncta obsolescent, small or interrupted.
Willistown, Pa. Rare.
Pl. 19, Fig. 24.
(pleura, a side, and sigma, the letter s)
Valve lanceolate, sigmoid; axial area very narrow, central area small; striæ punctate, in transverse and oblique lines.
Cleve divides the forms usually known as Pleurosigma into two genera, Pleurosigma and Gyrosigma. Pleurosigma includes all forms having oblique rows of puncta, while Gyrosigma includes all having longitudinal rows. Both have transverse striæ. The former consists entirely of marine species, while in the latter the species are found in fresh, brackish and salt water.
The endochrome in Pleurosigma, according to Mueller, consists of two bands which differ in the median part of each valve. Mereschkowsky says that the endochrome is so divided as to form four bands, two on each valve, that their position is different in different species, and that they are not the same on valves of the same frustule.
Cleve prefers to classify the species of Pleurosigma and Gyrosigma in accordance with the outline of the valve and the flexure of the median line. I shall, however, retain the method used by Peragallo and Grunow and arrange the forms according to the striation.
(1) Oblique Striæ about 90 Degrees, More Distinct Than the Transverse
PLEUROSIGMA FORMOSUM WM. SM.
Valve elongated, slender, gently sigmoid, acute at the ends; oblique striæ crossing each other at about 90 degrees; 10-16 in 10 µ; transverse striæ, 14-20 in 10 µ (Cleve).
Along the coast.
Pl. 22, Fig. 5.