LAMELLIBRANOHIATA. 529 
Fndodesma undosum.] 
Formation and locality Lower 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 H. gesneri occurs in the rocks of the state it will most probably be in the middle division of 
the Galena. 
ENDODESMA UNDOSUM, %. Sp. 
PLATH XXXVI, FIG. 38. 
Shell of the same general form as EL. 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 
of 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 EZ. gesneri Billings, sp., and E. orthonotum M. 
& W. sp., by its stronger lines of erowth, the irregular surface undulations, and 
more uniformly rounded posterior margin. 
Formation and locality.—‘‘Upper Buft Beds” of the Trenton formation, one and a half miles west 
of Beloit, Wisconsin, where it was collected by Mr. Charles Schuchert. f 
Mus. Reg. No. 8344. 
ENDODESMA COMPRESSUM, 1”. Sp. 
PLATE XXXVI, FIGS. 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 fig. 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 H. gesneri Billings, sp., than 
to any of the others. It is however readily distinguished by the broader sinuosity 
—34 
