ANATINID^. 145 



Shell oblong, nearly equivalve, slightly corapressed, attenuated 

 and gaping posteriorly, smooth, or minutely scabrous ; cartilage- 

 processes thick, not prominent, witli 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 T. distorta, 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 ; pallial sinus small, obtuse, triangular. Siphonal 

 orifices simple. T. concentrica, Bellevue. 



T. declivus, Reel., is the type of Ligula, which does not 

 appear to differ essentially from Rupicola. 



CALCARA, Recluz, 1868. (Periplom^-a, Conr.) Form t^^pical 

 of the Thracia3, 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 Aiiat. 

 ohlonga, Philippi. 



Periploma, Schumacher, 1811. 



Syn. — Anatina (partim). Lam. Bontia, Leach, Brown, 1844. 

 Gralaxura, Leach. 



Distr. — 12 sp. U. S., W. Indies, Panama, So, America. P. 

 insequivalms, Schum. (cviii, 57-59). 



Shell oval, very Inequivalve, inequilateral, sliglitly 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, deeplj' 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. TJ. S., Britain, Mediterranean. Fossil. Pliocene ; Sicily, 

 T. prsetenuis, Mont, (cviii, 60). T. Leana, Couth, (cviii, 61). 

 Hardly distinct from the typical group. 



PELOPiA, H. Adams, 1868. Shell oval, inequivalve, closed on 



