277 
Lorraine Faunas of New York and Quebec 
15. Pholadomorpha pholadiformis, Hall. 
{Plate II, Fig. 16; Plate V, Fig. 4) 
Cardinal and basal margins diverging at an angle of about 20 
degrees. Basal margin almost straight; at a point almost verti- 
cally beneath the beak it rises gradually toward the strongly 
rounded anterior margin. The latter extends 12 mm. anterior to 
the beak. Posteriorly the cardinal margin is fairly straight for 
about 35 or 40 mm. and then rounds gradually into the very ob- 
lique posterior margin, forming an angle of about 130 or 135 degrees 
with the latter. The margin is strongly rounded at the posterior 
extremity of the umbonal ridge. The umbonal ridge is low and 
very broad; it is moderately distinct for a distance of nearly 30 
mm. from the beak, but merges into the general convexity of the 
shell posteriorly. From this umbonal ridge the slope toward the 
basal margin and toward the cardinal margin is rather flat. There 
is no mesial sinus anterior to the umbonal ridge. The shell is 
concentrically striated. These striae are most distinct along the 
anterior half, below the umbonal ridge, and along the posterior 
half, above this ridge, where the low transverse plications are 
less distinct or absent. The transverse plications cover the 
slope beneath the umbonal ridge almost as far to the front as the 
area beneath the beak, although anteriorly these plications no 
longer reach the basal margin of the shell. They are approxi- 
mately vertical to the basal margin, although curving moderately 
forward on approaching the umbonal ridge. Similar low trans- 
verse plications may be detected along the cardinal margin from 
within 20 mm. of the beak to about 10 mm. beyond the point 
where the cardinal margin curves downward into the posterior 
margin of the shell. These plications form angles of about 70 
degrees with the cardinal margin, and the longest, posteriorly, 
scarcely extend more than 5 mm. from the cardinal outline. 
Along the basal margin, these plications number about 3 in a 
length of 5 mm. 
Locality. At the power house, about a mile southwest of the 
of Salmon River Falls, New York; in the upper areanaceous part 
the fossiliferous Lorraine. 
Essentially the same form occurs in the Lorraine at Gorrel 
Point, two miles northeast of the village of Gore Bay, on Mani- 
toulin Island, in Lake Huron. Fig. 16, on plate II, represents 
