MARINE MOLLUSCA OF THE UNITED STATES. 135 
cate behind. Beaks prominent, with an obtuse carination extend- 
ing to the angle of the posterior and basal margins; beak of the 
right valve perforated to receive the point of the left. Right valve 
more convex and extending somewhat beyond the left, and both 
slightly gaping. Hinge toothless, but with rounded eminences. 
Epidermis thin, with concentric undulated striz. Pallial impres- 
sion with an acute angular sinus. No ossiculum. 
New England, northwards. 
2. T. Myopsis, Beck. Fig. 303. 
Moller, Index Moll. Greenl. 18. 1842. 
T. Couthouyt, Stimpson, Bost. Proc., iv. 8. 1851. 
Shell small, white, orbicular-ovate, compressed; beaks nearly 
median, narrowed and rounded in front, more pointed and trun- 
cate behind, gaping; surface with rather elevated concentric lines ; 
hinge callus thickened backwards, without any distinct spoon- 
cavity. Ossiculum very minute. 
Height 17.5, length 25 mill. 
. 
New England, northwards. 
Mr. Jeffreys considers this species a synonym of 7. truncata, 
Brown (Brit. Conch. 1827), but I think that Brown’s figure rep- 
resents a very different shell. In thus adopting Brown’s name 
for this species, the following species, 7. truncata, M. and A., has 
its name preoccupied, and Mr. Jeffreys proposes to change it to 
T. septentrionalis (Ann. and Mag. Nat. Hist. 238, Oct. 1872). I 
do not adopt the new name because I am not satisfied that 
Brown’s species is really distinct from 7. distorta, Montagu. 
3. T. truncata, Mighels and Adams. Fig. 304. 
Bost. Journ. Nat. Hist., iv. 38, t. 4, f. 1. 1842. 
Shell small, ovate-triangular, compressed, white, rather solid ; 
beaks at posterior fourth, posterior margin broadly truncate. 
Beaks small, the right one excavated to receive that of the left 
valve. Epidermis yellowish, within white. Ligament rather 
large and prominent. Hinge callosity not spoon-shaped, produced. 
Height 12.5, length 19 mill. 
New England, northwards. 
See remarks under preceding species. 
Genus PANDORA, Bruguiere. 
Encyc. Meth. t. 250. 1792. 
Animal with mantle closed, except a small opening for the 
narrow, tongue-shaped foot; siphons very short, united nearly 
