250 Lamarck's Genera of Shells. 



The shell has been broken In three pieces, as shewn in the figure. 

 Its length is 19 inches, 2 lines, {French measure.) 2 Species.) 



4. Turrilites*. 



Shell spiral, turrited, multilocular, whorls contiguous, all visible ; 

 parietes articulated by sinuous sutures. Septa transverse, lobed 

 and indented at the circumference. Aperture rounded. 



The turrilites, instead of being discoidal, or simply arched, are 

 elongated, straight, and form a very elevated spiral, which, it seems, 

 must terminate in a point, like the turritella. Fragments of in- 

 ternal casts of this shell have been long known by the name of 

 turbinites. We are indebted for a more accurate knowledge of the 

 genus to M. Denis Montfort. 



One species. Turrilites costutalaf. 



Shell straight, turrited ; whorls convex, transversely ribbed ; 

 ribs tubercular at the extremities. St. Catherine's Hill, near Rouen. 

 PI. vi. Fig. 234. 



5. BaculitesJ. 



Shell straight, cylindrical, sometimes slightly compressed, rather 

 conical ; parietes articulated by sinuous sutures. Septa transverse, 

 near together ; disc of the septa imperforate, lobed and indented 

 at the circumference. 



The chambers of these shells, of which we have only the internal 

 casts are narrow, vansverse, and differ in that respect from those 

 of the turrilites, wb : h are rather longitudinal, the septa which 

 form them b i iirther asunder. In both, the chambers are 

 filled with ' matter. 



Type Aaculites Faujasii§. 



Shell straight, cylindrical, slightly depressed at the opposite 

 sides ; sutures lobed, indented. St. Peter's Mount, near Maastricht, 

 PI. vi. Fig. 235. 3 Species. 



Section II. 

 Monothalamous Cephalopoda. (1 Genus.) 



Shell unilocular, wholly external, and enveloping the animal. 



* From turrit, a tower. t Ribbed. t From baculum, a staff. 



§ In honour of M. Faujas. 



