448 



MANUAL OF THE M0LLU8CA. 



grooved with lines cf growth, and exhibits a distinct ligamonta] 

 ridge in each valve. 



In aged examples of R. calceoloides tho ligamental inlloction 

 is concealed, the cartilage pits partially filifcd up and ymoothod, 



j&'ig. 244. Upper view. Fig. 245. Side view. 



Internal mould of B. Heeninghavsii, Desm., j. Chalk. 



M, umbo of left valve; r, right umbo ; /, ligamental groove; c, c, cartilage ; a, ante riot 

 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. 



f^ub-genus ? Bi-radioliteSy D'Orbigny. R. canaliculatus 

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

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

 border<^d by two similar areas (a, a). Fossil, 5 species. Chalk, 

 France. 



Capri^ella, D'Orbigny. 



Type, 0. triangularis, Desm. (Fig. 246). 



Synonym, Caprinula (Boissii), D'Orbigny. 



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

 .*f a thick layer of open tubes, with a thin compact superficial 

 lamina ; cartilage internal, contained in several deep pits ; 

 •mibones more or less camerated ; right valve conical or elon- 

 gated, with a ligamental f\UTow on its convex side, and furnished 

 with one t>troiig hinge-tooth supported by an oblique plate : left 



