THE 
turned toward the shorter end of the shell, 
which is called the anterior end, and the oppo- 
site the posterior end. The ligament which 
holds the valves together is situated on the dor- 
sal margin, on the posterior side of the um- 
bones. The dorsal margin is also called the 
hinge line. The teeth just beneath the umbones 
are called the cardinal teeth, and the ones on 
either side, lateral teeth. Some bivalves have 
no teeth, and the valves are held together only 
by the ligament, and by the muscles of the 
animal. The length of bivalves is measured 
from the anterior to the posterior ends; the 
breadth from the dorsal to the ventral margin ; 
and the thickness from the centres of the closed 
valves. 
Class Pelecypoda consists of two orders; 
Siphonida and Asiphonida; five sub-orders ; 
forty-seven - families, and twenty-seven sub- 
families. 
ORDER SIPHONIDA. 
Animal with siphons, and mantle margin 
more or less closed. This order is divided into 
two sub-orders ;—Sinupalliata and _ Integri- 
palliata. 
SUB-ORDER SINUPALLIATA. 
Aninal with long siphons, partially or wholly 
retractile; the pallial impression upon the in- 
side of the valves having asinus. This sub- 
order has fifteen families. 
Family Gastrocheenidze, (Tubicolidze of La- 
marck), is divided into three sub-families, five 
- genera, ten sub-genera, and about forty species 
living, and as many more fossil. They are all 
burrowers in mud or stone, but do not inhabit 
the Atlantic coast of the United States. 
Family Teredidze has five genera and about 
forty species. These animals burrow in wood, 
floating logs, harbor piles, hulls of vessels, &c. 
They inhabit Norway, England, Pacific Ocean, 
&c. I haye never seen a specimen of any 
species in Rhode Island, although I have heard 
of specimens of Teredo being taken in New 
Bedford, Mass., from whale ships that had been 
: cruising ‘for years. 
* CONCHOLOGISTS’ - 
EXCHANGE. 19 
Family Pholadidze is divided into two sub- 
families; Pholadinz with nine genera and 
their sub-genera, and Jouannetinze, with five 
genera, &c. The animals of this family are all 
borers, and their shells are found imbedded in 
all kinds of material, such as Limestone, Chalk, 
Shale, Peat and Clay. 
SUB-FAMILY PHOLADIN-. 
Valves with an anterior gap, always open in 
adult shells. 
GENUS, PHOLAS, LINNAUS, 1757. 
There are only four species of this genus, 
three of which belong to the sub-genus Cyrto- 
pleura, Tryon, 1862. 
141.—Pholas costata, L. 
Shell large, thin inflated, oblong-ovate, white, 
covered with radiating toothed ribs. Length, 
six inches; breadth and heighth, each two 
inches. This:shell is very common in the West 
Indies and on the Atlantic Coast of the South- 
ern States. Itis sold in the markets of Ha- 
vana, and is highly esteemed as an article of 
food. The animal is phosphorescent and 
when alive shines in the dark. It is said that 
after eating this dainty, the lips of the eater 
appear to be on fire. Until 1845 a living speci- 
men of this species had never been found: within 
one thousand miles of New England, but Pro- 
fessor Adams had discovered a bed of dead 
shells of all sizes, at New Bedford, Mass., with 
indications that the living Pholads had inhab- 
ited these shores at no very distant period. In 
1845 Mr. Thomas A. Greene found several 
living specimens in the mud, brought up by the 
dredging machine, at the end of Long Wharf, 
in New Bedford. He thought they must haye 
burrowed two or three feet in the mud, Since 
that time no other living specimens have been 
discovered in New England, but as the ocean 
shore of Rhode Island has not yet been thor- 
oughly examined, the above facts would lead 
me to believe that there is a possibility of its 
yet being found here. 
142.—Pholas (Cyrtopleura), truncata, Say. 
Shell, chalky-white, oblong; beaks at the ° 
anterior third; anterior portion of the shell, 
triangular, pointed ; posterior broadly truncated. 
