88 MACGILLIVRAYIIDjE. 



Fam. MACGILLIVKAYIID^E. 



Lingual dentition closely resembling that of Risso'ella. 



Head with four, nearly equal, obtuse tentacles ; eyes ? 



Mantle inclosed, extended in front into a long, exserted 

 siphon. Foot large, expanded, truncate anteriorly, pro- 

 duced behind, and ? furnished with a float as in Ianthina. 



Operculum horny, annular, with a sub-central nucleus, 

 and strengthened by a straight rib. 



Shell horny, sub-transparent, globose, spiral. 



The animals constituting this group are not well known. 

 The explanation of the four apparent tentacles may perhaps 

 be found in supposing the two outer to be elongated eye- 

 pedicels, or by another supposition, that the two inner are 

 elongate lobes of a divided rostrum. The statement of the 

 Naturalist of H. M. S. Kattlesnake, to whom the typical 

 genus is dedicated, that the animal is possessed of a float, 

 and the structure and form of the shell, which bears some 

 analogy to Recluzia and Ianthina, together with the pela- 

 gian, gregarious habits of the animal, induce us to place 

 these creatures among the Heteropods. 



Genus MACGILLIVRAYIA, Forbes. 



Operculum thin, horny, semicircular, with concentric ele- 

 ments ; nucleus near the outer edge, with a straight rib con- 

 tinued nearly to the margin, and indicated externally by a 

 groove. 



Shell spiral, dextral, imperforate, thin, horny, globular, 

 transparent; spire obtuse; aperture oblong, entire, angular 



