414 Dr. J. E. Gray on a new Subgenus of Helicinadae. 



XXXV, — Notice of a New Subgenus of Helicinadse. 

 By Dr. J. E. Gray, F.R.S. 



There is an inclination, in several groups of Marine Univalve 

 Mollusca, for the animal to form a more or less deep notch or 

 fissure on the hinder part of the outer lip, as in the genera 

 Pleurotoma, Amphibola, Pleurotomaria, and Siliquaria; this 

 notch appears to be formed to facilitate the entrance and exit of 

 the water from the respiratory chamber. Sometimes the slit, or 

 a series of holes which may be considered as an interrupted slit, 

 is placed more in front, as in Haliotis ; or when the shell is sym- 

 metrical, as in Emarginula, it is in the centre of the front edge. 

 Some shells which are normally destitute of this notch are liable 

 to a malformation exhibiting it, as is the case in the common 

 Littorina littorea, 



I had never observed any indication of such a conformation 

 in any terrestrial mollusk until Mr. Damon of Weymouth kindly 

 showed to me some specimens of a species of Helicina he had 

 received from Cuba, under the name of Trochatella regina^ which 

 have this notch most perfectly developed, and as it indicates a 

 peculiar structure in the animal, I propose to separate it from 

 the group hitherto recognized in the family Helicinada, as a 

 distinct subgenus. Dr. Pfeiffer has considered it as forming a 

 peculiar section of the genus Trochatella, but none of the other 

 species of that genus show any inclination to this peculiarity. 



I may here remark, that some species of this family have a 

 notch or very narrow slit in the front of the outer lip near the 

 axis, but this slit appears to have no relation to the notches or 

 slit referred to in the other genera, being merely formed by a 

 process in the front of the outer edge of the operculum, a pecu- 

 liarity I have not observed in any other family of MoUusks. 



Hapata. 



Shell conical, subglobose ; spire conical, acute, whorls striated ; 

 aperture semiovate; outer lip expanded, with a deep sinus in 

 front and a deep wide notch in the hinder part of the outer edge. 

 Pillar-lip callous, straight in front, without any anterior slit. 

 Operculum half-ovate, annular, thin, horny ; nucleus in the 

 middle of the inner straight edge; covered internally with a 

 thick, smooth, shelly, callous coat. 



Hapata regina=Trochatella regina, Pfeiffer, Pneum. Mon.328; 

 Cat. Phanerop. Brit. Mus. 236. 

 Hab. Cuba. 



