270 PROCEEDINGS OF THE ACADEMY OF 



DESCRIPTION OF SOME NEW GENERA OF MOLLUSCA. 

 BY WILLIAM M. GABB. 



The following diagnoses of new genera are published in advance 

 of a more extended paper on West Indian mollusca, now in process 

 of preparation. The amount of material embodied in that paper is 

 so great, that circumstances will not permit me to illustrate the nu- 

 merous new species, and I avail myself of the present means of 

 explaining, by figures, the generic descriptions, which are not al- 

 ways clearly intelligible from verbal descriptions. 



PTEROPODA. 



Fam. LIMACINID^. 

 Planorbella, Gabb, pi. 11, fig. 2. 



Shell minute, vitreous, sinistral, apex sunken as in Planorbis. 



This genus, from its sinistral character, is evidently allied to 

 Limacina, from which its planorbiform mode of growth distinctly 

 separates it. The type P. imitans, were it dextral, might be mis- 

 taken for a very young specimen of Planorbis trivolvus, so nearly 

 does it copy the form of that shell. 



GASTEROPODA. 



MURICID.E. 

 Metulella, Gabb, pi. 11, fig. 3. 



Shell fusiform, canal more or less produced ; inner lip covered 

 with a thickened plate, continuous posteriorly with the outer lip. 

 Interior of both inner and outer lips strongly denticulated or 

 transversely striated. Surface cancellated or costate. 



This genus is more distinctly fusiform than Metida, and has the 

 additional character that the inner lip is covered throughout its 

 length by a series of prominent denticles, not necessarily corre- 

 sponding with the covered-up surface ribs. 



Type M. fusiformis. 



TURRID.E. 

 Glyphostoma, Gabb, pi. 11. fig. 4. 



Shell like Defrancia, but with the inner lip strongly cranulated 

 or transversely rugose. 



