THE - CONCHOLOGISTS’ - EXCHANGE. 
THE SHELL-BEARING MOLLUSCA OF 
RHODE ISLAND. | 
BY HORACE F. CARPENTER. 
Chapter XXXIX. 
Genus Zirphea Leach—1851. 
In Pholas, the dorsal margin is supplement- 
ed by two accessory plates; Zirphaea has a 
broader shell without accessory plates. It has 
but three species, one of which is common to 
the Atlantic shores of Europe and America. 
143.—Zirphea crispata, Linn. 
Synonyms : 
Pholas crispata, Linn and older authors: 
Pholas bifrons, Da Costa. Pholas latus, Lister. 
Solen crispus, Gmelin. Zirphzea crispata, all 
modern authors. 
Shell oblong-oval, thick and strong; valves 
touching only at the hinge, and at the middle 
of the base, gaping widely at both ends ; each 
valve is separated into two nearly equal parts 
by a broad furrow passing from the beaks to the 
base; the anterior half is covered with radiating 
toothed ribs. Length, two inches; height, one 
anda half.» It is common in all parts of North- 
western Europe, and in Northeastern America 
as far south as Cape Cod; very few specimens 
are found this side of the Cape. Very fine and 
large specimens are obtained at Nahant Beach 
in hard clay. 
SUB-FAMILY JOUANNETIN. 
Anterior ventral gap, closed in adults by a 
callous plate. 
There are five genera, seven sub-genera, 
and thirty-five species, none of which have yet 
been discovered in R. I. Martesia cuneiformis 
Say, and Diplothyra Smithii, Tryon, are found 
burrowing in oyster shells on the coasts of the 
Southern States. The former has been found 
at New Haven, Conn., by Dr. Perkins, and the 
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latter at Staten Island, and_as they occur boring 
into the Southern oyster, of which we plant 
thousands of bushels annually in our bay, it is 
among the possibilities that both these species 
might be inhabitants of Rhode Island. 
FAMILY SOLENID-E. 
Shell long, gaping at both ends; ligament 
external. This family is divided into two sub- 
families, Soleninze and Pharellinz. 
SUB-FAMILY SOLENIN Z. 
Shell ¢rzncated at both ends; umbones ¢e7- 
minal, withgne tooth in each valve. Siphon 
of the animal sort and wnted. There are six 
genera, two of which are fossil. The genus 
Solen, Linn, 1757, with thirty-seven species, is 
represented on the Atlantic coast of the U. 5S. 
by only one species, Solen viridis, Say, which 
inhabits from New Jersey to Florida. The 
| genus Ensis, Schum or Ensatella, Sw. with 
fourteen species is represented on our coasts by. 
144.—Ensatella Americana, Gould, 
In the twelfth edition of ‘ Systema Na- 
ture, page 1114, 1767, Linnzeus described an 
European shell which he called Solon ensis ; 
our species resembling it very much and con- 
sidered identical with it, has, until late years, 
been called by the same name. In 1817, Schu- 
macher discovered that Solen ensis was not a 
Solen; that genus having straight shells and 
| provided with one tooth in each valve, while 
| one valve and three 
these shells were curved and had two teeth in 
in’the other. Then he 
| proposed a new genus for these shells and called 
| ensis was not the European ensis at all. 
it Ensis, from the type species of the old genus 
Solen. Then its name became Ensis ensis. In 
1840 Swainson objected to calling the generic 
and specific names of shells by the same term, 
so he proposed the name of Ensatella, which 
was approved of and adopted by other author- 
ities. Then it read Ensatella ensis, but having 
got this point finally settled it seemed that our 
Gould 
was the first to notice the differences, but un- 
_ willing to make another change he called it pro- 
visionally variety Americana. All modern 
