44 THE NAUTILUS: 
which he calls Pyrgophorus; describing a number of new species 
from Nicaragua, probably all identical with either Pfeiffer’s or 
Morelets’ 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 defined in America. Pyrgophorus Ancey, must become a 
synonym of Potamopyrgus. 
THE SHELL-BEARING MOLLUSCA OF RHODE ISLAND. 
BY HORACE F. CARPENTER. 
FAMILY CYPRINID. 
This family contains but one genus 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 CARDITDZ. 
Five genera and over one hundred 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 Linné, 1758. 
There are about one hundred species, distributed world wide. 
The genus is divided by some authors into several sections, into 
one of which, Cerastoderma, falls the only species which inhabits. 
pals 
