40 Trans. Acad. Sci. of St. Louis. 



occur rarely here. A species identified as Liospira micula 

 which has not been recognized below the Utica in the 

 Minnesota region is abundant in this fauna and Liospira 

 progone which is not reported from below the Trenton 

 in Minnesota is represented by several specimens. From 

 the evidence furnished by this fauna the beds containing 

 it may be safely considered as pre-Trenton in age, but it 

 is not entirely clear whether they should be correlated 

 with the Black River or the Stones Eiver. 



Desceiption of Species. 



CTElSrODONTA AUBUENENSIS, U. Sp. 



PI, vii. f., 2-4. 



Shell small, four to seven millimeters in length, three to 

 five millimeters in height, length behind umbones slightly 

 greater than in front. Umbones prominent, beaks curved 

 inward and directed forward. Base regularly convex or 

 slightly flattened in the middle, antero-cardinal outline 

 slightly concave, posterior umbonal ridge straight to 

 slightly convex. Surface of shell marked with coarse, 

 well defined lines of growth. Number of teeth eighteen, 

 eight in front of the beaks. Teeth smallest near the beaks, 

 wanting beneath the beaks. Denticles nearly parallel to 

 a line drawn from the beaks through the greatest width of 



the shell. 



C. auhurnensis differs from C. fecunda, the nearest al- 

 lied species, in being smaller, proportionally much longer 

 in front of the beaks, narrower in proportion to the 

 length, and the denticles pointing away from the beaks at 

 a smaller angle. 



This species is based on a large number of specimens. 

 Number 11517 of the invertebrate paleontological collec- 

 tion of Walker Museum. 



CTENODONTA COSTATA, U. Sp. 



PI. vii. f. 7-8. 



Shell small, subtriangular, length and height subequal, 

 thickness about one-third the height, compressed near 



