448 MANUAL OF THE MOLLUSCA, 
grooved with lines of growth, and exhibits a distinct ligamenta] 
ridge in each valve. 
_ Im aged examples of R. calceoloides the ligamenta! inflection 
is concealed, the cartilage pits partially flisd up and smoothed, 
Fig. 244. Upper view. Fig. 245. Side view. 
Internal mould of #. Heninghausi, Desm., 3. Chalk. 
u, umbo of left valve; r, right umbo; J, ligamental groove ; c,c, cartilage; a, anterios 
adductor muscle ; a', posterior. i 
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. 
Pub-genus? Bi-radiolites, D’Orbigny. RR. ecanaliculatus 
(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). Jossil, 5 species. Chalk, 
France. 
CAPRINELLA, D’Orbigny. 
T'ype, ©. triangularis, Desm. (Fig. 246). 
Synonym, Caprinula (Boissu), 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; 
nmbones more or less camerated ; right valve conical or elon- 
gaved, with a ligamental furrow on its convex side, and furnished 
with one strong hinge-tooth supported by an oblique plate: left 
