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Contributions to Paleontology : 



same time, a difference of form among the hypostomae. Whether 

 these are all varieties of form of one species, may admit of some 

 doubt with our present means of comparison. It may be imprudent 

 to multiply specific designations for such remarkable forms as the 

 D. minnesotensis, and those presenting so many features in common 

 with that species. 



Plate iv, fig. 11, is a small specimen (one side of which has been restored 

 in the figure) from Lagrange mountain, Minnesota. 



Plate v, fig. 9. The glabella and fixed cheeks of a large individual from 

 Stillwater, Minnesota. 



In the latter specimen, the oblique truncation of the frontal limb on 

 each side is not so extreme as in the smaller individual; and from the 

 symmetrical contour still remaining, it appears as if separated along a 

 suture line. 



DIKELOCEPH ALUS PEPINENSIS. 



PLATE IV, FIGS. 1-4; AND PLATE V, FIGS. 13-17. 



Dikelocephalus pepinensis : Owen, Geological Report' of Wisconsin, Iowa and 

 Minnesota, page 574, Tab.l, f.9 & 9 a ; and Tab.l A, f. 7 ? 



Body comparatively narrow, subelliptical, wider anteriorly. 

 General contour of the head semielliptical, with ex- 

 tremely elongated cheek-spines. 



Glabella prominent, longer than wide, usually a little 

 narrowed anteriorly. Occipital furrow straight and 

 narrow : occipital ring broad, depressed convex, not 

 rising higher than the glabella in front of it. Posterior 

 glabellar furrow a little oblique at the extremities, and 

 straight in the middle : anterior to this furrow are two 

 slight indentations on each side of the glabella, near 

 the anterior limit of the palpebral lobe, which do not 

 reach to its summit. Dorsal furrow strongly defined, 

 and joining a wider furrow which limits the front of 

 the glabella. 



Fixed cheeks narrow, expanded in the direction of the 

 eye, and separated by a distinct groove from the palpe- 

 bral lobe ; posterior limb narrow, with the furrow 

 extending about half its length, and running out on the 



