512 THE PALEONTOLOGY OF MINNESOTA. 



[Earymya. 



Genus EUEYMYA, n. gen. 



Modiolopsis (part.) Hali. and Ulkich.. 



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 subabgular. No mesial sulcus, the surface of 

 the valves forward and dowiiward 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 preciselj^ as in Modiomorpha, Hall, but the Devonian shells, upon which that 

 genus is founded, have no posterior striated ligamental area, while in nearly e'very 

 other respect they agree with Modiolopsis. The new genus Modiolodon has one or 

 more strong Cardinal teeth in both valves, no ligameijtal area, an'd 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 E. plana, occurs 

 in the middle beds of the Treiiton 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 indiiferently 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. 



. 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, 



flg. 6; Ulrich, 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 



