93 GENUS XIX. NA UTILUS. 



The animal is supposed to be a kind of Sepia. 

 Linnaeus has described 17 species, Gmelin has added 7, 

 and Dr. Turton 7. Total, 31. 



Lamarck has divided this genus into 1 9, to which Mr. Par- 

 kinson has added 3, making- together 22, as follows : 

 Navtilus. a spiral, somewhat wheel-shaped univalve ; the 

 last whorl covering the others, the partitions of which 

 are simple ; the chambers numerous, formed by trans- 

 verse simple partitions perforated by a tube (see N. Pom- 

 pilius, f. 54). 

 Orbulites. Sljell spiral, somewhat wheel-shaped; the last 

 whorl envelops the others, and of which the internal part 

 is joined by sinuous sutures ; the transverse partitions are 

 pierced by a marginal tube (see N. Cornu Ammonis Iceve, 

 Bourguet Tr. des Petritic. t. 48. no. 311). 

 Ammonites. Shell spiral and wheel-shaped'; the turns con- 

 tiguous and all apparent ; the internal parts joined by 

 sinuous sutures. The transverse partitions waved, and 

 pierced by a marginal tube (see N. Cornu Ammonis. 

 Parkinson's Organ. Rem. 3. p. 133. t. 9. f. 5 to 9). 

 Planulites. Shell spiral and wheel-shaped, the whorls con- 

 tiguous, and all appearing and having the divisions sim- 

 ple ; the transverse partitions entire (see Bourguet's 

 Petrific. t. 46. f. 290.) 

 Nummulites. Shell lenticular and wheel-shaped ; the divi- 

 sions simple, covering all the whorls; chambers numerous. 



