Contributions to Palaeontology. 



97 



well characterized species in the higher beds of the 

 sandstone, and in the succeeding magnesian limestone. 

 The lower beds are especially characterized by the presence 

 of Conocephalites ; but I hesitate to admit, among these, 

 the occurrence of the Genus Dikelocephalus. Notwith- 

 standing the late determination by Dr. Shumard of the D. 

 latifrons from the lower beds, I cannot avoid the conclusion 

 that this too, with its " truncated conical " glabella, is a 

 Conocephalites. 1 In the intermediate beds, however, we 

 have the Dikelocephalus miniscaensis of Owen, which he 

 cites from the third Trilobite bed of F 1, two hundred or 

 two hundred and twenty feet below the top of that 

 formation. In all the specimens obtained, I have failed 

 to fiud one of this species with a facial suture corresponding 

 to typical Dikelochephalus, notwithstanding that some of 

 the specimens appear to preserve entire the central portion 

 of the cephalic shield. The direction of the suture is more 

 nearly as in Arionellus, and the places of the eyes more 

 anterior than in Dikelocephalus minnesotensis or D. pepinensis ; 

 while the cheek is short and broad, and much extended 

 at the posterior angle. It appears to me, therefore, that 

 this species should be admitted into the latter genus only 

 after satisfactory evidence of its character shall have been 

 obtained. The typical species, D. minnesotensis of Owen, 

 is cited as occurring in member d of F 1, " ninety or one 

 "hundred feet below the base of the Lower Magnesian 

 "limestone, near the margin of Lake St. Croix above 

 c< Stillwater ; towards the base of Lagrange mountain, 

 " and at the great slide below Lake Pepin, which is the 

 "fifth trilobite bed of the series of F 1." The D. pepin- 

 ensis found in the same association as the preceding. 



The interval between the lower beds at Mountain island, 

 and those in which these two species of Dikelocephalus 



^ee remarks under the generic description of Conocephalites. See 

 post. 



[Trans. v.~\ 13 



