130 SIXTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



apex^ abrnptly incnrved. Surface marked by lanaellose concern 

 trie striae; and^ when exfoliated, coarse radiating striae mark 

 ■ the surface of the cast "belexw the m-iddle. In some specimenSy 

 radiating striae are faintlj visible in the shell. 



The ovate valve associated with the spatulate form has a smooth 

 glossy surface, with fine concentric striae; and, when exfoliated^ 

 the surface of the cast is very distinctly striated by fine even or 

 somew^hat bifurcating stri9&. Should tl^isform prove to be distinct 

 from the spatulate one^ I propose for it the name Lingulepis ma- 

 tinalis. 



The species is common at the Falls of the St. Croix ; and eoarse sandy 

 layers, containing the same fossils, occur near the mouth of the Miniska 

 river in Minnesota. 



GENUS DISCINA ( Lamarck). 



Pr. Owen frequently cites Orbicula among the fossils of the 

 sandstone, and describes Orbicula jirima ; but the figures given 

 are not satisfactory. These fossils are cited from the St.Croix 

 falls, and upon specimens containing Lingula pinnaformis. So many 

 individuals are indicated (figures 13., 16, 17, 18 & 19), that it is 

 clearly a common fossil. Among a large collection made at the 

 locality in 1850, I have been unable to find a Discina; and I have 

 been disposed to believe that the broad convex liuguloid form, so 

 common in these beds, was at that time referred to Orbicula. 



In all the collections I have hut a single specimen which I refer, with 

 doubt, to Discina ; hut this is so obscure as scarcely to merit description. 

 It is from the later beds of the formation, and in the same association with 

 Dikelocephalus minnesotensis, at Mazomania, Wisconsin. 



DISCINA? INUTILIS (n.s.). 

 PLATE VI. EIG. 11. 



Shell small, elliptically subquadrate, concentrically striated : 

 apex excentric, nearly marginal. 



The specimen appears to consist of both valves, which in the pressure 

 have slipped a little out of place. My only reason for indicating this obscure 

 specimen, is, that Orbicula (Discina) has been regarded as a common 

 fossil of the Sandstone. 



