CONCHIFEKA. 



451 



Fossil y 10 species. Upper Greensand and Lower Chftlk. 

 Bohtemia, France, Texas. 



Fig. 251. Internal mould of CaprUina quadripartita, D'Orb., ^. 

 M, left umbo ; r, right umbo ; /, ligamental inflection ; c, cartilage ; t, t', dental sockets 

 a, a', position of adductors ; at e, a portion of txio tHird lobe is broken away.* From a 

 Bpecimen collected by ]Vir. Pratt. 



Caprotln'A, D'Oibigny. 



Type, C. semistriata, PI. XIX., Figs. 13 and 14. Le Mana, 

 Sarthe. 



Shell composed of two distinct layers ; valves alike in struc- 

 ture, dissimilar in sculpturing ; Hgamental groove slight ; 

 cartilage internal ; right valve fixed, striated, or ribbed, with one 

 narrow tooth between two deep pits, cartilage pits several on 

 each side of the ligamental inflection, posterior adductor sup- 

 ported by a plate : free valve flat or convex, with a marginal 

 umbo ; teeth 2, very prominent, supported by ridgos {apophyses) 

 of the adductor muscles (a a'), the anterior tooth connected with 

 a third plate {n), which divides the umbonal cavity. 



The smaller Caprotince occur in groups, attached to cyster- 

 shells ; their muscular ridges are much less developed than m 

 the large species (Fig. 251). C. costata is like a little Eadiolits. 



Fossil, 10 species. Upper Greensand, France. (The rest are 

 Chamas, &c.) 



Family IX. — TRiDACisriD^. 



Shell regular, equivalve, truncated in front ; ligament 

 external ; valves strongly ribbed, margins toothed ; muscular 

 impressions blended, sub-central, obscure. 



» The first and fourth lobss, those on each side of the hgomental inflection, appear 

 10 be the two divisions of a great iutcrual cartilage, like that of the Radiolite. (Figs 

 '^U, 245, c, c.) 



