288 



MANUAL or THE MOLLUSCA. 



valve conical or elongated, with a ligamental furrow on its convex side, and 

 furnished with one strong hinge-tooth supported by an oblique plate : left 

 valve oblique or spiral, with 2 hinge-teeth, the anterior supported by a plate 

 which divides the umbonal cavity lengthwise. 



In C. triangularis the umbonal cavity of the spiral valve is partitioned 

 off at regular intervals (Fig. 207, A) ; the length of the water chambers is 

 sometimes Z\ inches, and of the body-chamber from 2 to 7 diameters; speci- 

 mens measui'ing a yai'd across may be seen on the cavernous shores of the 

 islets near Rochelle.* {Pratt.) 



Fossil, 6 sp. Neocomian — L. Chalk. Frauce, Portugal, Texas. 





Fig. 210. C. Aguilloni, left valve. Fig 211. C. adversa (after D'Orb.) 



R. ff, position of adductors; I, ligament; u, umbonal cavity; /, tooth of fixed val re. 



broken off and remaining in its socket ; c, original point of attachment. 



Caprina, C. D'Orb. 



Etym. Caprina, pertaining to a goat. Si/n. Plagioptychus, Matheron. 



Ti/pe, C. AguiUoni, C. D'Orb. L. Chalk, Tyrol,* ( = C. Partschii, 

 Hauer.) 



Shell with dissimilar valves, cartilage internal; fixed valve conical, marked 

 only by Knes of growth and a ligamental groove ; hinge-margin with several 

 deep cartilage-pits ; and one large and prominent tooth on the posterior 

 side ; free valve obHque or spiral, thick, perforated by one or more rows of 

 flattened canals, radiating from the umbo and opening around the inner 

 margin ; anterior tooth supported by a plate which divides the umbonal 

 cavity lengthwise, posterior tooth obscure ; hinge-margin much thickened, 

 grooved for the cartilage. 



In C. adversa (fig. 211) the free valve is (.5) sinistrally spiral; its cavity 

 is partitioned off by numerous septa, and divided longitudically by the dental 

 plate. "When young it is attached by the apex of the straight valve (c), but 

 afterwards becomes detached, as the large specimens are found imbedded with 



* These singular fossils were called ichth^osarcoUtes by Desraarest, from their 

 resemblance to the flaky muscles of fishes. 



