100 



These observations induced me to place the family in my most 

 modern arrangement near OligyradcE. 



Mr. Cnming has kindly brought to me a specimen of the genus, 

 with its animal, which Mr. Salle discovered under leaves in the moun- 

 tains of Mexico, some distance from the sea. 



The species is aUied to Proserpina eolina, but differs in the spire 

 being mueh more convex ; I hence propose to call it P. Salleana. 

 Likę P. eolina, it differs from all the others I am acąuainted with in 

 the upper surface of the whorls being rugose, and only smooth on 

 the lower surface, as is the case \^ith many Nanina, showing, if the 

 smoothness and poUsh of the surface depend on the extension of the 

 mantle of the animal, the extension in this kind is coufined to the 

 under surface of the shell, as is proved by the examiuation of the 

 animal itself. 



This being the case, I am inclined to form this shell and P. eolina 

 into a new genus under the name of Ceres, characterized by the 

 roughness of the upper surface and the non-dilatation of the front 

 edge of the mantle, which is believed to be dilated in all the other 

 species of the true Proserpince. 



It will be seeu that most authors have placed these Mollusca either 

 with Helices or Oligyrce, and I was much iuclined to follow their 

 example, even after a cursory esamination of the animal itself. It 

 has much the external appearance of the animals of the lateral family, 

 having a short, broad, anuulated muzzle vvith a triaugular mouth, two 

 subulate lateral tentacles, with the eyes sessile on the outer side of 

 their base ; a moderately short foot, truncated in front, acute and 

 keeled above-behind, without any appearance of beards or any mem- 

 branous ridge on the sides ; the shell is slightly sunk into a cavity 

 in the front of the upper keeled part of the foot, as if it possessed 

 an operculum ; the edge of the mantle is free from the back of the 

 neck, producing an open nuchal respiratory cavity likę Cyclostoma 

 and Oligyra, and other operculated and unisexual land shells. 



"When the animal is more closely examined, it is found that there 

 is no operculum, the concavity on the front part of the foot into 

 which the under surface of the shell fits is furnished with a con- 

 tinuation of the mantle, having a raised crumpled edge evidently 

 capable of being expanded over the under surface of the shell, and 

 explaining the polished surface of this part of the shell ; — a structure 

 I have not observed in any other Mollusca. This extension of the 

 mantle might be mistaken for the mantle of the operculum, which, 

 as far as I know, is always quite distinct and separate from the 

 mantle of the shell, but in this animal the fringed edge of the con- 

 cavity is iu direct continuity with the true or shell-forming mantle, 

 both at the columnar and the outer external angle of the mouth of 

 the shell. 



The teeth of the lingual membrane are unlike those of Cyclostoma 

 and Helicina, which agree with those of Littorina and other marine 

 Rostriferous miivalves. The teeth resemble those of the ty picai 

 ItiphidoglosscE, as in the families Neritinidce, Tnrbonid(E, TrochidtB, 

 Roliolida, &c. All the Mollusca hitherto known belonging to these 



I 



