PLATE 16.
Genus—CORONULA.
- Fig. 1, rostrum, viewed from the inner side, of Coronula diadema.
- a, sheath, marked transversely in the upper part by the attachment of the opercular membrane.
- b, furrow on each side of (a), receiving the edges of the thick alæ of the adjoining lateral compartments.
- c′′, special plate, on which the alæ on their outer sides rest.
- d, radius, on the edge it may be just seen to consist of an outer layer (the normal radius), and a much thicker inner part (the pseudo or complementary radius) formed of oblique denticulated septa.
- e e′ e′′, basal edge of wall, which from its commencement at e, or e′′ can be followed, folding up to near the basal edge of the sheath, to its termination at e′′ or e.
- f, serrated lines of junction between the folds of the wall.
- 2, Lateral compartment of C. diadema, seen laterally, on a smaller scale than last fig., but taken from the same shell; letters of reference the same: this figure, if the ala a′ were removed, would do for a lateral view of the rostrum, or fig. 1.
- a, sheath, much foreshortened.
- a′, ala (therefore also part of sheath), and the edge of which fits into b of fig. 1.
- b, furrow receiving edge of ala of the adjoining carino-lateral compartment.
- c′′, special plate, seen edgeways.
- d, radius, the division into two parts, viz., the thin outer normal radius, and the under pseudo or complementary radius here shown (rather exaggerated) plainer than in fig. 1.
- e, basal edge of wall; to the right hand the three folds at their inner ends are seen obliquely, one behind the other: these are seen directly in front in fig. 1.
- 3, lateral compartment of C. balænaris, seen laterally; letters of reference the same as in last fig., but c′′ not introduced for this plate is barely developed, and only in the lower part, and is attached to the radius: g g points where fresh folds have been formed in the walls along the lines of suture, as may be seen in the outline of the wall in fig. 5.
- 4, lateral compartment of C. reginæ, seen laterally; letters of reference the same as in the last two figures.
- 5, Coronula balænaris, outline of the basal margin of the folded walls: s, s, the six sutures. The wall can be continuously followed from one end of a suture to the next suture.
- 6, Coronula diadema; small portion of the external surface of the wall, close to the basal edge, highly magnified; a, outer lamina, not extending down to the basal edge; b, inner lamina; c, projecting longitudinal septa.
- 7, Coronula diadema; transverse section through the upper part of the shell, showing the rostrum and the two adjoining lateral compartments (and the alæ of the carino-lateral compartments), all supposed to be a little separated from each other, so that the sutures, s s, are shown by white lines.
- A A A, rostrum.
- C C, lateral compartments.
- D D, carino-lateral compartments, of which only the alæ (a′) are shown.
- Of the letters in italics, those which occur in figs. 1, 2, 3, 4, 5, refer all to the same parts, viz.:—
- a, sheath, continuous with (a′) the alæ, where such occur.
- c′′, special plate on which the alæ rest.
- d, radius, divided into a thin outer normal radius, and the inner complementary portion, the latter shaded by convex lines of growth.
- d′ is a special tube (seen only as a black dot) for a thread of corium.
- e, folded walls.
- f, junction of the folded walls (see f, in fig. 1) leading into the cavities (f′) open beneath, and filled up by the epidermis (see Pl. 15, fig. 4) of the whale.
- h, inside of the transverse loops of wall, occupied by corium: in the enlarged section of a loop, in C. balænaris, in Pl. 15, fig. 2 a, the opposed sides are seen to be connected by shelly longitudinal plates.
- v, cavity occupied by the ovarian tubes and cæca.