78 Lamarck's Genera of Shells. 



contiguous, the last terminating in a straight line. Chambers ir- 

 regular, septa transverse, simple (no siphon) ; the last septum 

 pierced with from three to six holes. 



Small fossil shells ; the septa, which form the chambers, are at 

 unequal distances, and inclined to one another; some species have 

 scarcely one complete turn of the spiral. , 



Type. Lituolites nautiloidea *. 



Shell discoidal, caudate, ribbed; last septum with six or fewer 

 foramina. Fossil, Meudon. PI. vi. Fig. 216. 2 Species. 

 3rd Family. 

 Cristata. (3 Genera.) 



Shell semi-discoidal ; spire excentric. 



The cristata, are flattened, multilocular, shells, almost reniform, 

 or crested; the chambers gradually lengthen as they approach the 

 exterior, arched border, and appear to turn partly round an ex- 

 centric, more or less marginal, axis. 



1. Renulitesf- 



Shell reniform, flattened, furrowed, multilocular ; chambers 

 linear, contiguous, curved round a marginal axis, those farthest 

 from the axis, the longest. 



The form of these fossil shells is very remarkable. The chambers 

 are contiguous, unilateral, narrow, linear, curved into a portion of 

 a circle, all disposed in one plane in such a manner that the 

 first, or smallest, forms a little arc round a marginal axis, or 

 centre ; all the other chambers are ? placed on the same side as the 

 first, whence there results a flat, reniform, furrowed shell, having 

 its axis situated on the margin opposite to the convex part of the 

 chambers. 



One species. Renulites opercularis J. 



Shell semilunai , very flat ; furrows arched, concentric. Fossil, 

 Grignon. PI. vi. Fig. 217. 



2. Cristellaria §. 



Shell semi-discoidal, multilocular ; whorls contiguous, simple, 



* Nautilus-like. f From Ren, the kidney. 



I Opercular, i. e., resembling an operculum. 



§ From crista, a crest, or tuft. 



