518 THE PALEONTOLOGY OF MINNESOTA. 
LOrthodesma schucherti. 
OrTHODESMA SCHUCHERTI, ”. Sp. 
PLATE XXXVI, FIGS. 25 and 26. 
Shell only moderately elongate, subovate, between two and two and one-half 
times as long as wide; cardinal and basal margins nearly straight, gradually diverg- 
ing posteriorly to near the posterior end, where the hight is equal to once and a half 
times the hight at the beaks; posterior margin obliquely truncate above and rather 
strongly rounded in the lower half; the anterior end, though narrowly rounded, is 
still a little wider and shorter than usual for the genus. Umbones not prominent, 
less so than usual, compressed; beaks incurved, a little less than one-sixth of the 
length of the shell from the anterior extremity; umbonal ridge subangular and a 
well marked feature above, becoming obtuse and at last indistinguishable as it is 
traced to the postero-basal margin. Mesial sulcus undefined, obsolete, the surface 
anterior to the umbonal ridge being scarcely flattened. Surface with a very fine 
and a stronger set of concentric lines. Anterior muscular impression large, well 
defined, the inner side somewhat straightened, giving it a semicircular shape.|: 
This species, which, in the absence of a mesial sulcus, recalls Actimomya, is still 
so much like Orthodesma in all other respects that its generic position cannot be in 
doubt. Indeed, excepting the feature mentioned, the species is very similar to 
O. recta, the type of the genus. That species is more elongate and narrower poster- 
iorly, and has oblique folds on the cardinal slope not seen on the Minnesota form. 
The specific name is given in honor of Mr. Charles Schuchert, who found the 
only specimen seen. 
Formation and locality.—Middle Galena, Weisbach’s dam, near Spring Valley, Minnesota. 
Mus. Reg. No. 8343. 
OrTHODESMA SuBNASUTUM Meek and Worthen. 
PLATE XXXVI, FIGS. 23 and 24. 
Modiolopsis subnasuta MEEK and WORTHEN, 1870. Proc. Phila. Acad. Nat. Sci., p. 41; 1875, Geol. 
z Sur. Ill., vol. vi, p. 494. (Not Modiolopsis subnasuta Hall, 1860.) 
Modiolopsis carrollensis WORTHEN, 1882, Bull, No. 1, Ill. St. Mus. Nat. Hist. 
Shells rather small, elongate, narrow and slightly arcuate, the length a little 
more than two and one-half times the greatest posterior hight and more than three 
and a half times the hight at the beaks. Valves rather strongly convex, the most 
prominent part being on the well defined umbonal ridge a little behind and above 
the middle of the valves. Dorsal and ventral margins slightly diverging posteriorly, 
the former very gently arcuate, the latter with an equally slight and broad sinuosity 
chiefly anterior to the middle. Anterior end narrow, produced, rather sharply rounded 
