INTRODUCTION. 55 



the two latter of which alone are now received in cabinets 

 of shells, the four former belonging to that class of 

 microscopic fossils, now termed Foraminifera ; the genus 

 Nummulites, although large, may probably belong to 

 the same class, and perhaps it would have been better 

 to have included the remaining genus. Nautilus, in the 

 next family, from which it differs in having the septa 

 which -divided the chambers simple at their edges. 

 7. Ammonacea (plates, fig. 477 to 484). The edges of the 

 septa of these are all more or less sinuous and com- 

 plicated. This family contains the following genera. 

 Ammonites, Ammonoceras, Baculites, and Turrilites, 

 the latter of which presents a singular anomaly in 

 having an oblique spire, like that of the order Tracheli- 

 poda, while it is divided into chambers by sinuous septa. 



Order Monothalamous Cephalopoda. 



The only shells included in this order belong to the genera 

 Argonauta (plates, fig. 485), placed here by Lamarck, and 

 Bellerophon (plates, fig. 486 and 487), a fossil genus subse- 

 quently added. 



Order Heteropoda. 



The singular and beautiful transparent shell contained in 

 this order, under the generic name Carinaria, forms a cover- 

 ing to a small portion of an animal, equally remarkable and 

 equally distinct from those of all other orders. 



The above arrangement, although far from perfect, and 

 requiring numerous modifications, is perhaps liable to as few 

 objections as any other yet proposed, and will certainly be 

 more easily understood by those who have not the opportunity 

 of studying the soft parts of the animal. 



