506 T2J, PALEONTOLOGY OF MINNESOTA. 



[Uodiolopsis oweni. 



This species ought, perhaps, to go with Actinomya rather than Modiolopsis, but 

 as I have so far seen only the exterior of the shell, and therefore know nothing of 

 the internal characters, it seemed best to refer it to Modiolopsis provisionally, because 

 of a general resemblance to M. similis. I wish to say further, that I would not be 

 surprised "if the shell proved to have the hinge of a Cyrtodonta, several species of 

 which it resembles quite as much as it does Modiolopsis. 



Formation and locality.— Eea,i the base of the Trenton formation, Murfreesboro, Tennessee. 



Modiolopsis oweni, n. sp. 



PLATE XLII. PIGS. 15 and 18. 



This species is founded upon a single and not very well preserved cast of the 

 interior; It seems to belong to Modiolopsis and very near M. simiUs, with which 

 species it should be compared. As far as can be seen its valves were a little more 

 convex, the mesial sulcus narrower, the anterior part of the shell somewhat inflated 

 and the posterior part comparatively narrower. 



Formation and locality .—GsX^ua. Shales, aboiit five miles south of Cannon Palis, Minnesota. 



Modiolopsis aeguta, n. sp. 



PLATE XXXVI, EISS. 3-6. 



Shell small, ventricose, elongate, highest posteriorly, the length twice the 

 greatest hight, and three times the. hight at the beaks. Cardinal margin straight; 

 anterior end unusually long, sharply rounded at the extremity of the hinge beneath 

 which it slopes backward gradually curving into the straight ventral margin; poster- 

 ior end strongly convex and most "prominent in the lower half, above curving more 

 gently and very gradually into the dorsal edge. Beaks a little more than one-sixth 

 of the length from the anterior extremity, moderately prominent and incurved, com- 

 pressed; mesial impression scarcely miore than a mere flattening of the sides of the 

 shell; umbonal ridge rather sharply rounded. Point of greatest convexity of valves 

 very near the center. Surface with concentric lines, sharp, subequal and thread- 

 like on the cardinal slopes, here with about ten in 5 mm. at their strongest parts, 

 becoming faint before they pass over the umbonal ridge in their course to the 

 anterior end where they are again somewhat thread-like. In good casts of the 

 interior the anterior adductor scars are large, prominent, and marked on their inner 

 halves with transverse lines. The surface markings do not show through the, shell 

 so as to mark the casts. Hinge thin, apparently edentulous. An average specimen 

 is 24 mm. long, the largest seen about 31 mm. 



This is one of a number of closely related species ranging from the lower Trenton 

 to the middle beds of the Cincinnati group. They are all elongate, especially so for 



