ANATINIDA. 145 
Shell oblong, nearly equivalve, slightly compressed, attenuated 
and gaping posteriorly, smooth, or minutely scabrous; cartilage- 
processes thick, not prominent, with a crescentic ossicle; pallial 
sinus shallow. Outer shell-layer composed of distinct, nucleated 
cells. 
Animal with the mantle closed; foot linguiform; siphons 
rather long, separate, with fringed orifices; . gills single, thick, 
plaited ; palpi narrow, pointed. 
T. concentrica and 1. distor ta, Mont., are found in the crevices 
of rocks, and burrows of Saxicava; they have been mistaken for 
boring-shells. 
RUPICOLA, Bellevue, 1802. (Ixartia, Leach, 1852. Ligula, 
Recluz.) Shell irregularly suboval, hinge with a vertical 
cartilage-process; pailial sinus small, obtuse, triangular. Siphonal 
orifices simple. 7. concentrica, Bellevue. 
TY. declivus, Rech, is the type of Ligula, which does not 
appear to differ essentially from Rupicola. 
CALCARA, Recluz, 1868. (Periplomya, Conr.) Form typical 
of the Thraci, nearly equilateral, equivalve, hinge with a spoon- 
shaped cartilage-process in each valve directed anteriorly, pallial 
sinus deep. This name has been proposed for the fossil Anat. 
oblonga, Philippi. 
PerrpLomMa, Schumacher, 1817. 
Syn.—Anatina (partim), Lam. Bontia, Leach, Brown, 1844. 
Galaxura, Leach. 
Disir.—12 sp. U.S., W. Indies, Panama, So. America. ale 
inequivalvis, Schum. (eviii, 57-59). 
Shell oval, very inequivalve, inequilateral, slightly nacreous ; 
left valve deepest ; posterior side very short and contracted ; 
hinge with a narrow, oblique, spoon-shaped process in each valve, 
and a small triangular ossicle; an internal rib proceeds from 
under the hinge to the posterior margin; muscular impressions 
unequal, the anterior long and narrow, the posterior small, semi- 
lunar; pallial impression marginal. Siphons long and slender, 
separate. 
COCHLODESMA, Couthouy. Oblong, compressed, thin, slightly 
inequivalve ; umbones fissured; cartilage-processes prominent, 
ossicle minute; pallial sinus deep. Animal with a broad, com- 
pressed foot; siphons long, slender, divided throughout; gills 
one on each side, deeply plaited, divided by an oblique furrow 
into two parts, the dorsal portion being narrower, composed of 
a single lamina only, and attached by its whole inner surface. 
2 sp. U.S., Britain, Mediterranean. Fossil. Pliocene; Sicily. 
T. pretenuis, Mont. (eviii, 60). ZT. Leana, Couth. (eviii, 61). 
Hardly distinct from the typical group. 
PELOPIA, H. Adams, 1868. Shell oval, inequivalve, closed on 
