CONCH1FERA. 



279 



hey receive, and are sub-spiral, giving rise to bifid projections (c, c] on the 

 ;asts ; the single tooth in the left valve consists of two elements, and the 

 cavity (fossef) which receives it is divided at the bottom. 



Fig. 190. Diceras, J. Fig. 191. Requienia, 



Internal pasts : a, point of attachment ; c, c', casts of dental pits ; t, t' t furrows 

 produced by spiral ridges. (Mus. Brit.) 



REQUIENIA, Matheron. 



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



"Ex. R, Lonsdalii, PI. XVIII. fig. 12 and fig. 191, R. Ammonia, fig. 189. 



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

 ;ernal ; teeth 2:1; left valve spiral, its cavity deep, not camerated ; free 

 valve smaller, sub-spiral ; posterior adductor bordered by a prominent sub- 

 spiral ridge in each valve. 



The shell-structure of Requienia is like that of Ckama. The relative size 

 of the valves is subject to much variation ; in R. Favri (Sharpe) they are 

 nearly equal. The hinge-teeth are like those of Diceras ; the cavity for the 

 >osterior tooth of the right valve is very deep and sub-spiral (fig. 191, <?'). 

 Che internal muscular ridges are produced by duplicatures of the shell- wall, 

 and are indicated outside by grooves (fig. 189, }. In R. sub-cequalis and 

 Toucasiana there is a second parallel ridge, as in Hippurites and Caprotina. 



Fossil, 7 sp. Neoeomian L. Chalk. Brit. France, Spain, Algeria, 

 Lexas. 



