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). 



Brown Gem Clam 



Figure 85 



Parastarte triquetra Conrad 



Both sides of Florida (to Texas?). 



% 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 com- 

 mon 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 



