Contributions to Palaeontology. 



117 



distal extremity, which is pointed backwards. The hypo- 

 stomse associated with D. minnesotensis are very similar to 

 the hypostomse of Paradoxides. In the D. pepinensis we 

 have a facial suture as in D. minnesotensis, with a narrow 

 convex frontal limb ; while the pygiclium is narrow, promi- 

 nently convex in the axis, with a plain border of moderate 

 width. 



In the fragmentary condition of all the specimens, it becomes 

 exceedingly difficult to decide, in some instances, the limits of this 

 genus. The glabella in D. pepinensis preserves but indistinctly the 

 furrows anterior to the principal one crossing it. When carefully 

 examined, however, we find two faint indentations on each side of the 

 glabella, which may have been more considerable 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 Conocephalites and some 

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

 " obscure." In species like D. spiniger, where the glabella is slightly 

 narrowed 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 cha- 

 racters of species referred to Conocephalities j nor is it easy to 

 determine the limits of these genera, from the fragments in our 

 possession. 



DIKE LOGEPH ALUS MINNESOTENSIS. 

 PLATE IV. FIGS.5-10; PLATE V; AND PLATE VI. 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 "broad, semielliptical, with the posterior angles of the 

 cheeks prolonged. 



Glabella moderately convex, longer than wide, or as long 



