LAMELLIBRANCHIATA. 529 



Undodosma undosum.] 



Formation and locality.— Lo'^&i Trenton limestone, Dunleith, Illinois. There is reason to believe 

 the species occurs in Minnesota and it will be well to search for it in the limestone at Minneapolis and 

 St. Paul. If E. gesneri occurs in the rocks of the state it will most probably be in the middle division of 

 the Galena. 



Endodbsma undosum, n. sp. 



PLATE XXXVI, FIG. 38. 



Shell of the same general form as E. orthonotum M. and W., sp., being elon- 

 gate, with the length a little more than twice and a half the hight; dorsal and 

 ventral margins subparallel; posterior edge almost uniformly rounded; anterior 

 end short, narrowly convex. Beaks depressed, wide, strongly incurved; umbonal 

 ridge inconspicuous; mesial depression undefined, wide, rather shallow. Lunule 

 narrow but shaply defined. Ridge and sulcus rather distinct in the anterior half 

 Df the posterior dorsal slope of casts. Surface of casts with numerous strong and 

 somewhat irrregular concentric lines of growth; on the dorsal slope and umbonal 

 ridge a number of large and very irregular undulations or depressions. 



This species is distinguished from E. gesneri Billings, sp., and E. orthonotum M. 

 & W. sp., by its stronger lines of growth, the irregular surface undulations, and 

 more uniformly rounded posterior margin. 



Formation and locality. — "Upper Buff Beds" of the Trenton formation, one and a half miles west 

 of Beloit, Wisconsin, where it was collected by Mr. Charles Schuchert. 



Mus. Reg. No. 8344. 



Endodesma oompressum, n. sp. 



PLATE XXXVI, PIGS. 35 and 37. 



Shell elongate, dorsal and ventral margins subparallel, the length two and one- 

 half times the hight. Anterior margin concave above, most prominent and suban- 

 gularly bent down at the middle, beneath which point the upper part of the 

 gradual curve into the basal line is nearly vertical; ventral outline very broadly 

 sinuate; posterior margin oblique, most prominent and strongly rounded in the 

 lower half, above passing rather gradually into the hinge line. Beaks compressed, 

 mesial depression or sulcus illy defined but very wide, causing the sinuosity of 

 the ventral margin to extend farther posteriorly than usual. Umbonal ridge 

 rather sharply defined on the upper side by the distinctly concave character of 

 the dorsal slope. Dorsal edge inflected, the inflected part extending rather far 

 inward under the beaks- (see flg. 37). Lunule narrow, deep and well defined. 

 Surface of cast with a few obscure concentric undulations. 



This species seems to be more nearly related to E. gesneri Billings, sp., than 

 to any of the others. It is however readily distinguished by the broader sinuosity 



-34 



