STYLIOLA. 53 



Sub-gen. pleuropus, Eschscholtz, 



Sides of the mantle with elongated tentacular processes. Shell 

 conical. 



pellucida, Eschsch. 



Genus BALANTIUM, Leach. 



Shell triangular, depressed, transverse, waved ; mouth 

 oblong, narrow, oblique, without any lateral slits. 



Ex. B. recurvum. Children, pi. 6, fig. 4. Shell, B. re- 

 eurvum, fig. 4, a. 



Balantiwn has a simple conical shell, curved at the end, 

 and compressed from before backwards ; B. recurmim, one 

 of the handsomest of Pteropods, has a steady mode of 

 swimming by lateral movements of the fins, and does not 

 flit about in the water in such a lively manner as the 

 CavolinKE. They are met with only in small numbers at a 

 time, and do not make their appearance until after sunset. 



Species of Balantium. 



australe, D'Orh. recurvum, Children. 



inflatum, Eyd. and Soul. rugosum, UOrh. 



Genus STYLIOLA, Lesueur. 



Body elongate, conical, rounded. 



Shell elongate, conical, subcylindrical ; mouth larger 

 than the cavity, without any lateral slits. 



Syn. Cresis, Rang. Crisia, Menke. 



Ex. S. subulata, Quoy and Gaimard, pi. 6, fig. ^,- ^^, 

 Shell, S. subulata, fig. 5, a. /%^<^^^^C^j 



