Lorraine Faunas of New York and Quebec 
279 
part of the Lorraine section, as here interpreted. It will be 
necessary to collect the specimens in order to assign them to their 
proper species, now that the presence of several species of this 
type is suspected. 
It is scarcely necessary to state that the group of species typified 
by Modiolopsis pholadiformis does not belong to the genus White- 
avesia, as typified by Whiteavesia cincinnatiensis, Hall and Whitfield 
The striations of the latter are narrow and more or less radial, 
while the plications of the Modiolopsis pholadiformis group, 
along the basal margin, are broad and more or less transverse to 
the longitudinal axis of the shell, and posteriorly are more or less 
divergent from the umbonal ridge. For the latter the designa- 
tion Pholadomorpha is here proposed, with Modiolopsis pholadi- 
formis as the type. 
16. Pholadomorpha pholadiformis — divaricata v 
{Plate II, Fig. 14) 
Basal margin forming an angle of about 18 degrees with the 
cardinal margin; this results in a remarkably narrow outline 
anteriorly, which may be due in part to compression. Posterior 
margin very oblique, rounding gradually into the cardinal margin, 
and much more rapidly into the basal outline. Shell concen- 
trically striated, but the conspicuous ornamentation consists of 
the low, broad, transverse plications characteristic of the species. 
These plications cover the lower slope of the shell, from the basal 
margin to the crest of the umbonal ridge, from the lower posterior 
angle to the anterior muscular area. The shell as a whole appears 
to have been shorter, and more convex; posteriorly the plicatiors 
are much more oblique to the basal margin, especially toward the 
umbonal ridge which they approach here with a strong forward 
curve; toward the middle of the shell this forward curvature be- 
comes less pronounced, and near the beaks the plications are al- 
most vertical. Along the cardinal margin the low transverse 
plications are nearly vertical for a distance of about 2 mm., 
posteriorly, and then curve rapidly forward on approaching the 
umbonal ridge. Even along the upper part of the posterior mar- 
gin, these low transverse plications curve first obliquely down- 
ward and then much more strongly forward on approaching the 
