BALCH: LIST OF MARINE MOLLUSCA. 
159 
Rather uncommon on soft bottom, 3-4 fath. 
Gemma purpurea H. C. Lea. Venus gemma Totten. Smith 
and Prime (’70), p. 388. Tottenia gemma Verrill (’73), p. 682. 
Locally abundant, lying on the surface of black mud and fine 
gravel on the fiats. 
var. manhattensis Prime. Venus m. Smith and Prime (’70), 
p. 388. Tottenia m. Verrill (’73), p. 682. S. 
A few specimens so identified occurred capriciously among the 
G. purpurea. Rare. 
Petricolidae. 
JPetricola pholadiformis Lam. Smith and Prime (’70), p. 390. 
Verrill (’73), p. 680. S. 
Common, boring in the salt marsh among roots of grass, etc., at 
top of beach. 
Caediidae. 
Cardium pinnulatum Conrad. Smith and Prime (’70), p.387. 
Verrill (’73), p. 683. N. 
One live and several dead specimens on hard bottom in 6 fath. 
Rare. 
Liocardium mortoni (Conrad). Cardium m. Smith and Prime 
(’70), p. 387. Laevicardium m. Verrill (’73), p. 683. S. 
Abundant in soft mud at and below low water. 
• 
Myidae. 
My a arenaria Linn6. Smith and Prime (’70), p. 390. Verrill 
(’73), p. 672. 
Abundant but not large. In the marsh before mentioned (see 
under Modiola plicatula) occurred a distorted variety, heavy, trun¬ 
cated, and gaping, which resembled the circumpolar My a truncata 
Linn, almost exactly, even to the tough and persistent epidermis. I 
think it would scarcely be distinguished from specimens of M. trun¬ 
cata lacking the epidermal tube. Perhaps adverse circumstances in 
both cases have produced parallel results. Doubtless the thick 
epidermis is a protection from the acids of the marsh. 
