540 THE PALEONTOLOGY OF MINNESOTA. 
[Cyrtodonta affinis. 
different cardinal teeth. In all these respects the shell agrees much better with 
an authentic example of C. carinata Billings, now before me, and as both the 
Palwarca ventricosa of Hall and the Cyrtodonta subcarinata of Billings are from the 
Trenton limestone in the northern part of Lake Huron, they are probably indentical. 
Formation and locality.—Lower Trenton limestone Dunleith, Illinois; Beloit, Janesville and Mineral 
Point, Wisconsin; Cannon Falls and Minneapolis, Minnesota. 
CyrTopvonTa oBLIQUA Meek and Worthen. 
PLATE XXXIX, FIGS. 35 and 36. 
Cypricardites obliquus MEEK and WORTHEN, 1868, Geol. Sur. Il1., vol. iii, p. 311. 
Of this species I have seen only the original type figured and described by 
the authors. Their figures being unsatisfactory, it seemed worth the while to 
prepare others, especially as the species may at any time be found within the 
limits of the State. It is to be looked for in the middle and lower beds of the 
Galena in Fillmore county. The type specimen is from the Galena at Scales 
Mound, Illinois, and is now preserved in the Illinois State Museum. 
CYRTODONTA AFFINIS, 2. sp. 
PLATE XXXIX, FIGS. 20-23. 
Shell small, rather compressed convex, obliquely subovate, alated and much 
the highest posteriorly. Dorsal margin straight or very gently arcuate, rather long, 
not passing gradually into the broadly and uniformly rounded posterior margin, the 
junction being obtusely angular; ventral margin but little convex, ascending rapidly 
to the small and narrowly rounded anterior end. Beaks small, projecting very little; 
umbones compressed, due to a flattening of the antero-ventral slope; umbonal ridge 
moderately distinct in the upper half; cardinal slope gently concave; greatest 
thickness on the umbonal ridge above and a trifle in front of the center of the 
valves. Surface with fine indistinct concentric striz and distinct sublamellose lines 
of growth. Hinge of moderate thickness; cardinal teeth small, short, four in each 
valve; posterior lateral teeth very slender, four in the right valve. Muscular im- 
pressions rather faint, not well determined. Length 20 mm.; posterior (greatest) 
hight 15 mm.; anterior highest 10 mm.; entire thickness 6.5 mm. 
A variety reappears in the middle Galena. This is relatively more convex and 
not quite as high posteriorly. Length 15 mm.; hight 10 mm.; thickness 7 mm.. It 
may be distinguished as var. fillmorensis. 
The typical form of this species is associated and was at first confounded with 
Matheria rugosa. Aside from the hinge, which is of course very different in the two 
forms, the Matheria is distinguished by its much shorter, subtruncate anterior end. 
