526 THE PALEONTOLOGY OF MINNESOTA. 



[Endodesnia ouneatum. 



of sinuate. Endodesma finally is separated from all true Modiolopsidce 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 Bhytimya, 

 Ulrich, which is regarded as an early type of the Pholadellidce. 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 gr"oup of species and its 

 development in times succeeding the Trenton to which all the species how known 

 are restricted. 



Six species of Endodesma are illustrated in this work. Besides these, Modiolop- 

 sis ? ttentonensis (Conrad) Hall, is almost certainly also referable to the genus. 



Endodesma ouneatum, n. 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 

 umbonal 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 E. trentonen&e 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 E. gesneri Billings, sp., but in other respects these 

 two species are quite distinct. 



Formation and locality.— ThQ specimen figured, which is the only one seen, was discovered by Dr. C. 

 H. Bobbins in the middle Galena near his home at Wykofi, Minnesota, and kindly given to the author for 

 description. 



