138 SIXTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



In tlie fragmentary condition of all the specimens, it becomes exceedingly 

 difficult to decide, in some instances, tlie limits of this genus. The glabella 

 in D. pepinensis preserves but indistinctly the furrows anterior to the prin- 

 cipal one crossing it. When carefully examined, however, we find two faint 

 indentations on each side of the glabella, which may have been more con- 

 siderable in the crust than appear in the cast. In the D. minnesotensis, I 

 have failed to observe more than a single indentation on each side, anterior 

 to the furrow which crosses the glabella. The posterior furrow is oblique at 

 its extremities, as in the glabellar furrow of ConocepHx\lites and some 

 others : the second furrows, according to the generic description, are 

 " obscure." In species like D. spimger, where the glabella is slightly nar- 

 rowed anteriorly, and the posterior furrow is deeply impressed at the sides 

 and less strong in the middle, while the second one is conspicuously marked 

 at the sides and faintly across the glabella, with a faint anterior furrow, we 

 have a close approach to the characters of species referred to Conocepha- 

 LiTES ; nor is it easy to determine the limits of these genera, from the 

 fragments in our possession. 



DIKELOCEPHALUS MINNESOTENSIS. 



PLATE IX, FIGS. 5-10; PLATE X; AND PLATE XI, FIGS. 1, 3 & 4. 



Dikelocephalus minnesotensis : Owen, Geol. Report Wisconsin, Iowa and Minnesota, page 



574, Tab. 1, f. 1, 2, 10 ; and Tab. 1 A, f. 3 & 6. 



Body large, somewhat quadrilateral, convex in the middle, with 

 the sides and extremities depressed or flattened. 



Head broadJ^semielliptical, with the posterior angles of the cheeks 

 prolonged. 



Glabella moderately convex, longer than wide, or as long in front 

 of the occipital furrow -as the width ; sides parallel ; front 

 rounded. Occipital furrow comparatively narrow and well de- 

 fined, with a wide, nearly flat or little convex occipital ring. 

 The posterior glabellar furrow crosses the glabella as far from 

 the occipital furrow in the middle as the width of the occipital 

 ring, and curves forward so as to terminate a little behind the 

 anterior limit of the palpebral lobe. Anterior to this furrow 

 there is on each side a shallow groove, reaching about one-third 

 across the glabella. 



The facial suture cuts the anterior contour in a nearly vertical line 

 from the outer limb of the palpebral lobe, and is thence directed 

 inwardly in a slightly curved line to the anterior limit of the 

 palpebral lobe : thence turning almost rectangularly outwards, 

 it curves gently downwards into the posterior limb of the 

 cheek, at a distance from the dorsal furrow of five-sixths the 



