448 



MANUAL OF THE MOLLUSCA. 



grooved with lines of growth, and exhibits a distinct ligamental 

 ridge in each valve. 



In aged examples ot H. cakeoloidea the ligamental inflection 

 is concealed, the cartilage pits partially filled up and smoothed, 



Fig. 244. Upper view. Fig. 245, Side view. 



Internal mould of R. Haninfjhausii, Desm., ^. Chalk. 



K, umbo of left valve ; r, right umbo ; I, ligamental gi'oove ; c, c> cartilage ; a, anterior 



adductor muscle ; a', posterior. 



and the teeth and apophyses so firmly wedged into their re- 

 spective cavities, as to suggest the notion that the valves had 

 become fixed about a quarter of an inch apart, and ceased to 

 open and close at the will of the animal. 



Fossil, 42 species. Neocomian — Chalk. Texas; Britain, 

 France, Bohemia, Saxony, Portugal, Algeria, Egypt. 



Sub-genus ? Bi-radiolites, D'Orbigny. E. canaliculatus 

 (Fig. 225, upper valve). Ligamental groove visible in one or 

 both valves, sometimes occupying the crest of a ridge, and 

 bordered by two similar areas (a, a). Fossil, 5 species. Chalk, 

 France. 



CaprinellAj D'Orbigny. 



Type, C. triangularis, Desm. (Fig. 246). 



Synonym, Caprinula (Boissii), D'Orbigny. 



Shell fixed by the apex of the right valve, or free ; composed 

 of a thick layer of open tubes, with a thin compact superficial 

 lamina ; cartilage internal, contained in several deep pits ; 

 umbones more or less camerated ; right valve conical or elon- 

 gated, with a ligamental furrow on its convex side, and furnished 

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



