144 BOOK OF SPECIES. 



POLYSTOMELLA. 



^hell discoid, multilocular ; whorls contiguous, not 

 apjmrent externally, radiated exteriorly by stricB 

 or costa running in the direction of the whorls; 

 aperture of many holes variously disposed. 



P. CRispus. W. 18. 8. 



VORTICIALIS. 



Shell discoidal, spiral, multilocular; whorls con- 

 tiguous, not apparent externally; septa trans- 

 verse, imperforate, not extending from the 

 centre to the periphery ; aperture marginal. 



V. STRIGILATA. W. 13. 41. 



NAUTILUS, 



Discoidal, spiral, multilocular; parietes simple, 

 without any suture; whorls contiguous, the 

 last enveloping the sutures; chambers numerous, 

 narrow, transverse, formed by transverse septa^ 

 last chamber very large ; septa concave on the 

 side next the aperture, their discs perforated 

 by a tube, and their margins very simple. 



N. POMPiLius. Sub-orbicular^with the whorls 

 smooth both on the back and sides; aperture 

 oblong, heart-shaped; umbilicus concealed; white, 



