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PETRICOLIDAE 419
Color whitish to tan with purpUsh over the beak and posterior areas. PaUial
sinus commonly, but not always, about the length of the posterior muscle
scar. It points upward. This is a very common shallow-water species. A
number of subspecies or forms have been described, but their vahdity needs
clarification: purpurea Lea (fig. 84c to e), ?nanhattensis Prime and fretensis
Rehder.
Genus Parastarte Conrad 1862
Shell the size of a split-pea, very similar to Geimna. In Parastarte, the
ligament is high and situated beneath the beak, occupying a very high and
broad area. In Gemma, the ligament is very narrow and elongated, and ex-
tending posterior to the beaks. PaUial sinus much smaller in Parastarte.
Figure 85. Brown Gem Clam, Parastarte triquetra Conrad, ^ inch (Florida).
Parastarte triquetra Conrad
Both sides of Florida (to Texas?).
Brown Gem Clam
Figure 85
% inch in size, very similar to Gemma geTfmta, but much higher than
long, with the beaks larger and elevated. Exterior highly polished and
smoothish. Color usually tan to brown, but may be flushed with pink in
beachworn specimens. The pallial sinus is almost absent. Moderately common
on sand bars and obtained by screening the sand.
Family PETRICOLIDAE
Subfamily PETRICOLINAE
Genus Petricola Lamarck 1801
Subgenus Naranio Gray 1853
Petricola lapicida Gmelin Boring Petricola
South half of Florida and the West Indies.
H inch in length (up to 1% inches in the Lesser Antilles), ovate, in-
flated, chalk-white, with criss-cross, threaded sculpturing. Beaks swollen and