450 



MAIOJAL OF THE MOLLTJSCA. 



chamber from 2 to 7 diameters ; specimens measuring a yard 

 across may be seen on the cayernous shores of the islets neai 

 Rochelle.* (Pratt.) 



jPosst7, 6 species. Neocomian — Lower Chalk. France, Portngal, 

 Texas. 



Fig. 249. C. Af/idllojii, left valve 



Fig. 250. C. adversa (after D'Orb.). 



a, a, position of adductors ; I, ligament ; u, umbonal cavity ; t, tooth of fixed valve, 

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



Caprin-a, C. D'Orbigny. 



Etymology, caprina, pertaining to a goat. 



Synonym, Plagioptychus, Matheron. 



Type, C. Aguilloni, 0. D'Orbigny. Lower Chalk, Tyrol 

 (=0. Partschii, Hauer). 



Shell with dissimilar valves, cartilage internal ; fixed valve 

 conical, marked only by lines 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 

 oblique 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. 250) the free valve is {h) sinistraUy spiral ; 

 its cavity is partitioned off by numerous septa, and divided 

 longitudinally 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 the 

 spire downwards. (Saemann.) The lower valve of (7. Cog-wa^icZiaria 

 is sub-spiral. 



* These singular fossils were called ichthyosarcolites by Desmarest, from their 

 resemblance to the flaky muscles of fishes. 



