COlSrCHIFEEA. 



451 



Fossil, 10 species. XFpper Greensand and Lower Chalk. 

 Bohemia, France, Texas. 



Fig, 251. Internal mould of Caprotina quadripartita, D'Orb., |. 

 M,left umbo ; r, right umbo; I, ligamental inflection ; c, cartilage ; t, V, dental sockets 

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

 specimen collected by Mr, Pratt. 



Capeotina, D'Orbigny. 



Type, 0. semistriata, PI. XIX., Figs. 13 and 14. Le 'Mans, 

 Sarthe. 



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

 ture, dissimilar in sculpturing ; ligamental 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 ridges {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 oyster- 

 shells ; their muscular ridges are much less developed than m 

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



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

 Chamas, &c.) 



Family IX. — Tridacjiod^. 



Shell regular, equivalve, truncated in front ; ligament 

 external ; valves strongly ribbed, margins toothed ; muscular 

 impressions blended, sub-central, obscure. 



* The first and fourth lobes, those on each side of the ligamental infection, appear 

 to be the two divisions of a great internal cartilage, like that of the Eadiolite. (Figs 

 244, 245, c, c.) 



