526 THE PALEONTOLOGY OF MINNESOTA. 
[Endodesma cuneatum. 
of sinuate, Hndodesma finally is separated from all true Modiolopside by the lunule 
in front of the beaks and the sulcus and ridge on each side of the hinge line. 
A more natural placement of the genus seems to me to be near Rhytimya, 
Ulrich, which is regarded as an early type of the Pholadellide. But as Endodesma 
evidently is a complex primitive type with characters suggesting widely different 
Lamellibranchiata it is probably good policy to defer coming to a final conclusion 
as to its position until we know more of the origin of the group of species and its 
development in times succeeding the Trenton to which all the species now known 
are restricted. 
Six species of Hndodesma are illustrated in this work. Besides these, Modiolop- 
sis? trentonensis (Conrad) Hall, is almost certainly also referable to the genus. 
ENDODESMA CUNEATUM, 7”. Sp. 
PLATE XXXVI, FIGS. 33, 34. 
Shell elongate, the length and greatest hight, which is subcentral, respectively 
as nine is to four. Valves strongly convex, the point of greatest thickness on the 
umbonai ridge above and in front of the center; cuneate posteriorly. Dorsal mar- 
gin gently arcuate, passing rather gradually into the posterior outline; the latter is 
prominent and sharply rounded near the middle, nearly straight in the upper half 
and slightly convex below; ventral margin gently convex in the posterior half, 
straight or barely sinuate. near the center of the anterior half, and rather strongly 
convex in front: anterior end short, most prominent and narrowly rounded in the 
middle, very slightly concave in the upper half. Beaks of moderate size, strongly 
incurved, with a rather distinct lunette beneath them; mesial sulcus clearly defined; 
umbonal ridge unusually prominent, subangular near the beaks. Cardinal slope 
abrupt, concave, in casts of the interior showing a well marked curving depression 
and ridge on each side of the hinge line. Surface of cast with a few obscure con- 
centric folds. Anterior muscular scar very faint, situated just within the anterior 
extremity of the shell, of semielliptical shape, the inner side straight. 
This species must be closely related to LE. trentonense Hall sp., from the Trenton ~ 
of New York, but in the figure of that species the anterior end is quite different, 
being shorter and obliquely truncate. The anterior end of the Minnesota form is 
more like that of the Canadian EH. gesneri Billings, sp., but in other respects these 
two species are quite distinct. 
Formation and locality.—The specimen figured, which is the only one seen, was discovered by Dr. C. 
H. Robbins in the middle Galena near his home at Wykoff, Minnesota, and kindly given to the author for 
description. 
