200 CHAMIDJE. 



for the insertion of the anterior muscle. D. PouecM, Munier- 

 Chalmas. Cret. ; France. 



Requienia, Matheron, 1842. 



Dedicated to M. Requien, author of a Catalogue of Corsican 

 Mollusca. 



Distr. — Fossil, 7 sp, Neocomian — L. Chalk ; Britain, France, 

 Spain, Algeria, Texas. B. Lonsdalii, Sowb. (^cxvii, 8, 9, 12). 

 B. ammonia, (cxvii, 10, 11). 



Shell thick, very inequivalve, attached by the left umbo ; liga- 

 ment external ; teeth 2'1 ; left valve spiral, its cavity deep, not 

 concamerated ; free valve smaller, subspiral ; posterior adductor 

 bordered by a prominent subspiral ridge in each valve. 



The shell-structure of Requienia is like Chama. The relative 

 size of the vah^es is subject to much variation ; in B. Favri 

 (Sharpe) they are nearly equal. The hinge-teeth are like those 

 of Diceras ; the cavity for the posterior tooth of the right valve 

 is very deep and subspiral. The internal muscular ridges are 

 produced by duplicatures of the shell-wall, and are indicated 

 outside by grooves. In B. suhsequalia and Toucasiana there is 

 a second parallel ridge, as in Hippurites and Caprotina. 



The following uncharacterized groups are probably not very 

 distinct from Requienia. 



TOUCASiA, Munier-Chalmas, 1813. T. carinata, Matheron. 

 Urgonian. 



MATHERONIA, Muuier-Chalmas, 1813. M. Virginise, Sc. Ur- 

 gonian. 



ETHRA, Matheron. E. Manieri, Math, Urgonian. 



Capeina, C. d'Orbigny, 1823. 



Etyni. — Caprina, pertaining to a goat. 



Syn. — Sphrerucaprina, Gremm. Plagioptychus, Matheron, 

 1842. Gemmellaria, Munier-Chalmas. 



i)zsi!r.— Fossil, 10 sp. Upper Greensand and Lower Chalk; 

 Bohemia, France, Texas. 



Shell with dissimilar valves, with subspiral beaks ; fixed 

 valve conical, marked only by lines of growth and a ligamental 

 groove ; hinge-margin with several deep cartilage-pits ; and one 

 large and prominent tooth on the posterior side ; free valve 

 oblique or spiral, thick, perforated by one or more rows of 

 flattened canals, radiating from the umbo and opening around 

 the inner margin ; anterior tooth supported by a plate which 

 divides the umbonal cavity lengthwise, posterior tooth obscure ; 

 hinge-margin much thickened, grooved for the cartilage. 



In C. adversa (cxvii, 18; cxviii, 19) the free valve is sinis- 

 trally spiral ; its cavity is partitioned off by numerous septa, 

 and divided longitudinally by the dental plate. When young it 

 is attached by the apex of the straight valve, but afterwards 



