CONTRIBUTIONS TO CONCHOLOGY. 



JVC 2. 



Descriptions of supposed new species and varieties of Helictdae 

 from Jamaica, by C. B. Adams, Professor &c. in Amherst College, 

 Massachusetts. Oct. 1849. 



Geomelania. Pfr. To the single species which Dr. Pfeiffer 

 made the type of this new genus, we have the pleasure of adding two 

 or three, all of which are of much less size. They have the same gen- 

 eral facies, in respect of form, truncation, and sculpture, except in the 

 spiral striae of G- elegans, as well as the most essential generic char- 

 acters of G. Jamaicensis, Pfr. None of the new species however ex- 

 ceed Dr. PfeifFer's species in the development of the generic charac- 

 ters, and his species remains therefore the most appropriate type, as 

 which its superior size gives it a practical advantage. 



It is a matter of profound regret, that the question of the existence 

 of an operculum is not yet definitively settled. Of G minor a multi- 

 tude of individuals were seen in various stages of decay and many in a 

 fresh state, but without the animal. No operculum was seen in any 

 specimens, nor were there occuring loose with the shells any oper- 

 cula, which could have belonged to them. So far as an opinion can 

 be formed without a living individual, it seems very probable that the 

 genus is not operculated. Indeed its affinites with Cylindrella are 

 such, that we were at first disposed to regard these shells as an aber- 

 rant group of that genus. They resemble it in the great degree of 

 truncation, in the general form, in the sculpture, and even in the ap- 

 erture, for some Cylindi'ella; are slightly efiuse. It is not to be forgot- 

 ten however, that the shells of Geomelania also closely resemble those 

 of Truncatella. But the inland habits of the species render it very 

 probable that the animals have little affinity with a maritime genus. 



Since this genus is little known, we commence with a description of 

 the typical species, from a specimen in the Cumingian Collection, for 

 the loan of which and of several other rare or unique specimens of 



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