To^K ., «,- . . , LAMELLIBBANOHIATA. " 615 



Technophorus fllistriatus.] 



very obscure linear depression. The entire rostrum also is somewhat constricted, 

 presenting an appearance that may have been produced by a slight internal thick- 

 ening of the shell, extending from the anterior to the posterior umbonal rib. Two 

 curved folds, the posterior one the strongest, extend from the postero-ventral angle 

 toward the beaks, becoming indistinguishable, however, about midway between the 

 two points. Surface markings and hingement unknown. 



Length 11.5 mm., bight 6.8 mm., convexity of one valve about 2.2 mm. 



This incompletely known species is very similar-in both the outline and general 

 expression to T. pundostriatus Ulrich, from the middle beds of the Cincinnati group in 

 Ohio and Kentucky. Though doubtless closely related, a careful comparison of internal 

 casts — the only condition in which the present species is known — proves that they can 

 be separated, the Minnesota species having the beaks more anterior and more prom- 

 inent, the anterior margin more uniformly rounded, and the post-cardinal outline 

 more concave, while the posterior ridges are more oblique and do not, as is the case 

 in casts of the Cincinnati shell, extend beyond the middle of the distance to the beaks. 

 None of the other species are near enough to require comparisons. 



Formation and locality. — The specimen described was found in the upper part of the Trenton lime- 

 stone at Minneapolis, Minnesota. The same piece of stone contains numerous specimens of Orthis perveta 

 Conrad, and Zygospira (Hallina) nicolteti W. and S. 



Technophorus filistriattjs Ulrich. 



PLATE XL, FIGS. 35 and 36. 



Technophorus fllistriatus Ulkich, 1892. Amer. Geol., vol. x, p. 101. 



Shell small, though large for the genus, compressed, with the greatest convexity 

 in the anterior half, scarcely alate posteriorly, the hight and length as three is to five. 

 Beaks small, projecting very little, slightly incurved, one-third of the entire length 

 of shell from the anterior extremity. Anterior end much the widest, broadly and 

 uniformly rounded except above where the curve turns rather sharply into the hinge 

 line. Ventral margin rounded in front, straight and sloping upward in the posterior 

 half to the acute extremity. Posterior margin short, apparently straight and 

 sloping forward, cardinal margin straight, except for a slight prominence in the 

 region of the beaks. Anterior half of surface marked with closely arranged, 

 thread-like, concentric lines, between which small puuctae are obscurely visible 

 on the specimen described. These markings seem to be wanting in the posterior 

 half, only a few obscure growth lines being visible here. Posterior ridge sharp 

 and strong, very gently curved in its course from the beak to the produced 

 lower angle of the posterior extremity of the shell. Between this ridge and a line 

 drawn vertically across the shell from the beaks, the surface is depressed, forming a 



