BEEDE: NOTES ON CAMPOPHYLLUM TORQUIUM. 189 
Monopteria gibbosa alata. var. nov. 
Shell small, not very gibbous; beak extending a trifle beyond 
the hinge-line. Prominent on account of lunule, but not:much 
elevated, and placed well back for this genus; umbonal ridge less 
prominent than in any other species of this genus and less curved. 
Posterior ear very greatly developed, about equalling the entire 
body of the shell in area. Antero-dorsal margin sinuate on ac- 
count of the turning down of the margin to form the lunule; anter- 
ior margin circular nearly to the postero-ventral extremity of the 
shell, which is-acute; the posterior margin consists of a broad shal- 
low sinus, extending from the postero-ventral end to the point of the 
ear which is apparently rounded and obtuse. The ear is not sep- 
arated from the shell by a distinct depression, but slopes gradually 
from the umbonal swell, save to the extreme lower edge where the 
depression is more abrupt. Very fine, concentric lines of growth 
are visible, all of which pass around the shell with a double curve 
to the ear, where they again curve backward, and then forward to 
the hinge-line. Length2o0 mm., depth 18mm., convexity of single 
valve a trifle less than 4 mm. 
This shell differs from J. gibosa M. and W. to which it is most 
closely related in some respects, in being much less gibbous, ear 
much larger and more obtuse, antero-dorsal outline more sinuous, 
umbonal ridge much straighter and less prominent, beak placed 
farther back and depression separating the ear from the umbonal 
ridge more shallow. These characters, if permanent, are amply 
sufficient upon which to base a species, but I refrain from assigning 
specific importance to them until more material has been studied. 
As a means of distinquishing the form I suggest the above varietal 
name. 
It differs from MJonotis sp? Keyes* in being more round on the 
anterior margin and more sinuate on the antero-dorsal margin; ear 
about twice as large, depression separating the ear from the 
umbonal ridge less distinct; beak placed farther back; postero- 
ventral extremity more acute, and the umbonal ridge a little less 
prominent, though of about the same degree of curvature. 
In figure 5, herewith given (twice natural size), the artist has 
represented the hinge-line as slightly curved, which gives the beak 
undue prominence. The margin 1s embedded in the matrix and 
the shell is too thin and frail to admit of its removal. The artist 
followed the outline as it appears in the matrix. 
*Geol, Surv.. Mo. vol. v. pl. xlvi, Wig. 10. 
