512 THE PALEONTOLOGY OF MINNESOTA. 
[Eurymya. 
Genus EURYMYA, n. gen. 
Modiolopsis (part.) HALT and ULRICH. 
Shell thin, short, compressed, high and subalate posteriorly, greatly narrowed 
anteriorly, transversely truncate-ovate or subtriangular in outline. Cardinal margin 
straight, base oblique, gently convex. Beaks small, near the anterior extremity. 
Umbonal ridge moderate, rounded or subangular. No mesial sulcus, the surface of 
the valves forward and downward from the umbonal ridge being slightly convex or 
flat rather than concave. Hinge strong, with a broad longitudinally striated liga- 
mental area posterior to the beaks, and beneath them an obscure cardinal fold or 
tooth in the left valve and a corresponding depression in the right. Muscular 
impressions and pallial line apparently as in Modiolopsis. 
Type: Modiolopsis plana Hall. 
The alate appearance of the postero-cardinal region, rounded base, absence of a 
mesial depression, and the presence of a striated ligamental area are the principal 
distinguishing features when compared with Modiolopsis. The anterior part of the 
hinge is precisely as in Modiomorpha, Hall, but the Devonian shells, upon which that 
genus is founded, have no posterior striated ligamental area, while in nearly every 
other respect they agree with Modiolopsis. The new genus Modiolodon has one or 
more strong cardinal teeth in both valves, no ligamental area, and a mesial thicken- 
ing of the inner sides of the valves that produces mesial sulci on the casts. 
Besides the type only one other species has been described that I would place in 
this genus without question. This is the Modiolopsis alata Ulrich, from the hill quar- 
ries at Cincinnati, Ohio. A third form, if it is really distinct from EZ. plana, occurs 
in the middle beds of the Trenton in Kentucky and Tennessee. A possible fourth 
species is the Modiolopsis truncata Hall, a rare shell of the Cincinnati rocks. This 
species is known only from indifferently preserved casts of the interior. So far as 
these admit of judgment, the species might well be classed with Eurymya. Of the 
hinge nothing is known beyond this, that it was stronger than usual for Modio- 
lopsis. f 
Eurymya pLana Hall. 
PLATE XXXVI. FIGS. 27 and 28. 
Modiolopsis plana HALL, 1861. Rep’t. Sup’t. Geol. Sur. Wis., p. 30; Geol. Wis., vol. i, pp. 38 and 438, 
fig. 6; Unnicu, 1892, Nineteenth Ann. Rep. Geol. Nat. Hist. Sur. 
Minn., p. 224. 
Shell rather small, compressed, subtriangular in outline, alate and highest 
posteriorly, the greatest hight and length (the latter measured parallel with the 
hinge line) respectively as six is to seven. Cardinal margin straight, nearly as long 
