518 THE PALEONTOLOGY OF MINNESOTA. 



[Orthodesma sell ucherti . 



ORTHODESMA SCHUCHERTI, n. sp. 



PLATE XXXVI, FIGS. -J5 and 20. 



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 Adinomya, 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 

 0. 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 tubnasuta MEKK and WOKTHEN, 1870. Proc. Phila. Acad. Nat. Sci., p. 41; 1875, Geol. 



Sur. 111., vol. vi, p. 494. (Not Modiolopsis subnasuta Hall, 1800.) 

 Modiolopsis carrollensie WOKTHEN, 1882, Bull. No. 1, 111. 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 



