Lorraine Faunas of New York and Quebec 285 
A second specimen, numbered 2086, is labelled as coming from 
the Plunk River, at Chambly, Quebec. Although only about 42 
mm. in length, it shows the post-umbonal plications very well. 
This species is long and narrow, and has the subparallel cardi- 
nal and basal margins as in Orthodesma, especially that group of 
species represented by Orthodesma curvatum. However, the post- 
umbonal plications are much more suggestive of some species of 
Modiolopsis belonging to the Modiolopsis concentrica group. This 
form of ornamentation is unknown in Orthodesma but is frequent 
in Modiolopsis; for instance in Modiolopsis arguta and Modiolopsis 
obsoleta. Compared with these shells, however, the height of the 
shell is less enlarged posteriorly. If we have not misinterpreted 
this species it combines the characteristics of two genera, usually 
easily differentiated. 
/ ^ 
21. Orthodesma approximatum, sp. nov. 
{Plate I, Fig. 5) 
Shell possibly closely related to Modiolopsis postplicata, but 
differing in the absence of conspicuous plications on the post-um- 
bonal slopes. If this species is an Orthodesma it belongs to the 
Orthodesma curvatum group. The cardinal margin is slightly 
curved posteriorly. Excepting near the beak, the umbonal ridge 
is distinguished only faintly from the general convexity of the 
shell, and the mesial sulcus is nearly obsolete. The surface is 
marked by faint concentric striations and wrinkles which are most 
distinct below and anterior to the beak. Along the post-umbonal 
slopes, when held in a very oblique light, very faint concentric 
wrinkles, about 8 or 9 in a length of 5 mm., may be seen, but it is 
difficult to imagine these as suggesting identity of the form here 
described as Orthodesma approximata with Modiolopsis postpli- 
cata. The position of the anterior muscular scar and of the adja- 
cent part of the pallial line, for a distance of about 10 mm., is 
distinctly indicated. The general appearance of the shell is 
smoothish. From the cardinal side of the umbonal ridge, near 
the beak, a low angulation extends backward, gradually deviating 
from the cardinal margin, until at a distance of 30 mm. from the 
beak it is fully 2.5 mm. from this margin. Above this angulation 
the surface along the cardinal margin is concave, as though the 
