CONCHOLOGY. 103 



whorls of the spire slightly visible in an umbilicus projecting 

 interiorly from the summit. 



B. naiicum. The seanut Bulla. 



Species thin ; the whorls of the spire visible externally, 

 but without projection, and with a suture as if caniculated 

 without thickening at the anterior part of the columellar edge. 



B.fragilis. The fragile Bulla. 



Species very thin, rather involute ; the whorls of the spire 

 distinct within as without ; the suture deep, angular, and cleft 

 in a greater or less part of its length. 



FAMILY V. 



Aplysiacea. Two genera. 

 1. Aplysia. Three species. 

 This genus may almost be said to have no testaceous cov- 

 ering, as it appears more like the element of a shell. 



Aplysia depilans. Aplysia fasciata. 



A. punctata. 



A. depilans. The bald Aplysia. 



Shell dorsal, semicircular, of a thin yellow cartilaginous 

 substance. 



2. Dolabella. Two species. 



Closely allied to the Aplysia; it is a singularly formed shell, 

 difficult to describe, as it contains few of the characteristics 

 which distinguish other shells. 



Shell rudimentary, entirely flat, sub-spiral, with a summit 

 thick and very callous. 



Dolabella Rumphii. Dolabella fragihs. 



D. Rumphii. Rumphius's Dolabella. 

 Base thick, callous, and sub-spiral ; dilated above, thin, and 

 wedge-shaped. 



