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CHESTNUT HILL, PHILADELPHIA, PA., FEBRUARY, 1888. 
No. 8. 
THE SHELL-BEARING MOLLUSCA OF 
RHODE ISLAND. 
BY HORACE F. CARPENTER. 
Chapter XLII. 
Genus Macoma, Leach, 1819. 
This genus contains eighty-five species, one 
of which inhabits New England, south of Cape 
Cod, and another from Cape Cod north to 
Greenland. Our species is the 
164.—Macoma fusca, Say, 1826. 
Syns : 
Psammolia fusca, Say. 
Sanguinolaria fusca, 
Migh., Stimp. 
Tellina fusca, Phil. 
‘¢  Greenlandica, Beck. 
‘¢ ~ solidula, Pult., Hanley, Midd. 
« zonata, Dill. 
«rubra, DaCosta. 
«  Balthica, Linn, Phil. 
Macoma fusca, Tryon, W. G. Binn., Dall., ete. 
Con., Gould, DeKay, 
Shell thin, compressed, ovate-orbicular, sub- 
equipartite, rounded before and narrowed and 
a little pointed behind; beaks small, ligament 
external ; there are two unequal parallel teeth 
in each valve, the large one grooved. Color, 
variable, according to locality. Length, one 
inch; height, four-fifths ; breadth, two-fifths. 
Linnzeus, in 1767, in his Systema Nat., page 
1120, described a small rose-tinted shell which 
he called Tellina Balthica Most of the above 
synonyms are probably of his species. It 
might or might not be our species which he de- 
scribed, and not being certain, we adopt Say’s 
name, as next in order of time, and as we 
know just what species he meant by his de- 
scription in Jour. Acad. Nat. Sci., Phila., V. 
220, 1826. It inhabits from Georgia to Green- 
land. It is one of the most common species in 
Rhode Island. Dead specimens can be seen 
at all times at Field’s Point, and sometimes 
even as far up as Red Bridge, on the Leekonk 
River. It lives in sand or mud, just below the 
surface, near low-water mark. They are found 
on all our shores, but most abundantly in the 
Barrington and Warren Rivers. In_ those 
slimy, muddy, treacherous spots, where every 
step brings to the surface bubbles of carburetted 
Hydrogen gas, from the gradual decomposition 
of vegetable matters, they are as black as ink ; 
in the inlets of salt marshes, and near where 
fresh water empties into the bay, they attain 
their largest size; these specimens are quite 
thick and are covered with a dark, rusty epi- 
dermis in clean, quiet sandy places, or showing 
through their semi-transparent epidermis the 
tints of lemon or of rose. 
FAMILY PETRICOLID. 
This group consists of four genera and 
about fifty species. They are mostly borers 
in clay or soft rock, and are irregular in 
form. 
Genus Petricola, Lamarck, 1801. 
There are thirteen species, one of which in- 
habits the whole Atlantic coast of the United 
States. 
165.—Petricola pholadiformis, Lam. 
Syns : 
7 
Petricola fornicata, Say, Russell. 
«  dactylus, Say, Gould. 
Shell long, ovate-cylindrical, equivalve, very 
inequipartite, chalky white within and without; 
