Class VI. NAUTILUS. SAIL-SHELL. 245 



Sect. III. UNIVALVE SHELLS. 



* With a regular spire. , , 



GENUS XIX. NAUTILUS. SAIL-SHELL. 



Shell univalve, consisting of compartments or 

 cells, communicating 'with each other by 

 means of perforations in the sepia or par- 

 titions. 



* Spiral ; spires or volutions connected. 



Lin. Tr. \ni. 114. Mont. Test. Br. igi. t. 6. 1. LACUS- 



/. 3. id. Sup. 88. TRis. 



* N. with a spiral shell, compressed, umbili- 

 cated, ridged ; of three spires, above convex 

 and connected, apertures half oval; partitions 

 three rayed, perforated ; diameter one fourth 

 of an inch. Fresh water. 



On flags and carkes in Ke7it and Biickuig- 

 hamsliwe. ■ 



