Fig. 332.—Interior of the same, seen from the dorsal side, showing brachial spires. (After Hall.)
In Leptaena (Fig. [334]) the occlusor scars (a) in the ventral valve are narrow and median, and are enclosed by a pair of flabelliform divaricator impressions (d.v); in the dorsal valve two pairs of occlusor scars (a.a, p.a) are well marked, and accessory posterior occlusor scars are traceable in some specimens. The vascular sinuses (v.s) and genital areas are conspicuous in many species of this and other genera.
Fig. 333.—Productus giganteus. (After Woodward.) Carboniferous Limestone. A, Interior of dorsal valve. B, Interior of ventral valve. C, Transverse section of valves. D, Hinge line of A: a, occlusor scars; d, divaricator scars; i, “reniform impressions”; ca, cardinal process; h, hinge line; p, brachial prominence; s, cavity for spiral arms; do, dorsal valve; ve, ventral valve.
In Waldheimia (Fig. [329]) a sub-umbonal “peduncular muscle” scar (p) in the ventral valve has before it a pair of “accessory divaricator” scars (a.d) flanked by a pair of “ventral adjustor” (v.a) and a pair of “divaricator” impressions (d), between which lie the two occlusor scars (a). In the dorsal valve anterior and posterior pairs of occlusor scars (a.a, a.p) are visible.
The minute structure of the calcareous shell of the Testicardines is of flattened fibrous prisms inclined at a very acute angle to the surfaces. In many forms minute tubes more or less closely arranged pierce through the fibrous shell-substance; but in some genera (Productus) they do not reach the outer surface (see p. [468]). Allied genera, however, differ much in the punctate or impunctate character of the shell.
Fig. 334.—Leptaena rhomboidalis. (Silurian.) A, External view of ventral valve. B, Interior of ventral valve: a, occlusor scars; d, pseudo-deltidium; d.v, divaricator scars; c.a, hinge area; t, teeth. C, Interior of dorsal valve: a.a, anterior occlusor scars; p.a, posterior occlusor scars; c.a, hinge area; c.p, cardinal process; d, chilidium; s, dental sockets; v.s, vascular sinuses.
Synopsis of Families