44 THE XAUTILUS. 



which he calls Pyrgophorus ; describing a number of new species- 

 from Nicaragua, probably all identical with either Pfeifter's or 

 jNIorelets' forms, the latter being apparently unknown to him. About 

 a pint of these Nicaragua shells were sent to the writer a year or 

 more since ; the variability shown by them is extraordinary, and 

 renders it doubtful whether more than one species of Potamopyrgus 

 can be detinetl in America. Pyrgophorus Ancey, must become a 

 synonym of Potamopyrgus. 



THE SHELL-BEARING MOLLUSCA OF RHODE ISLAND. 



BY HORACE F. CARPENTER. 



FAMILY CYPRINID.E. 



This family contains but one genns and that genus but one 

 species. This species, Cyprina Islandica, inhabits from the eastern 

 end of Long Island to the Arctic Ocean, and from thence southward 

 to England. It is said to have been found off Block Island in 29 

 fathoms' water, but is hardly entitled to a place in the •' Shell-bear- 

 ing Mollusca of Rhode Island." 



FAMILY ISOCARDIID^. 



Three genera and twenty-three species, not represented in 

 America, by living species, but there are several fossil species. 



FAMILY CARDIID^. 



Five genera and over one hundi'ed and fifty species, is repre- 

 sented in R. I. by two genera, each with a single species. The 

 shells constituting this family are called Cockles. They abound' 

 in shallow water in sandy places and are used for food. They 

 are also found in deeper water. One species, Cardium edule is col- 

 lected in immense numbers in Great Britian, where they take the 

 place of clams, which are as rare with them as Cockles are with us. 



Genus Cardium Linne, 1758. 



There are about one hundred species, distril)uted world wide. 

 The genus is divided by some authors into several sections, into 

 one of which, Cerastoderma, falls the only species which inhabits 

 R. L 



