CONTRIBUTIONS TO PALEONTOLOGY. 141 



BIKELOCEPHALUS MINNESOTENSIS, var. LIMBATUS. 



PLATE IX. FIG. 12. 



A single fragment shows the anterior part of the glabella, and 

 nearly the whole of the frontal limb. In this specimen the antero- 

 lateral angle of the frontal limb is more rounded, and the anterior 

 margin elevated in a distinct border which does not appear to be 

 thickened. Within this border are a few wrinkled striae, directed 

 towards the glabella. In a single small individual from Lagrange 

 mountain, I have seen a similar but less defined border. 



Without other specimens, I am unwilling to indicate this as a distinct 

 species. It occurs with D. minnesotensis and D. pepinensis, at Lagrange 

 mountain. 



DIKELOCEPHALUS MINNESOTENSIS, var. 



PLATE IX, FIG. IX; AND PLATE X, FIG. 9. 



General form of head and glabella as in D. minnesotensis. Glabella 

 moderately convex, and slightly narrowing in front of the eyes. 

 Occipital furrow straight : posterior glabellar furrows oblique -, 

 the anterior one slightly marked, and nearly straight. The frontal 

 limb is rounded at the antero-lateral angles, and slightly extended 

 in the middle. 



The marked difference between this form and the D. minnesotensis is in 

 the frontal limb, which is extended in the middle so as to interrupt the 

 continuous curve of the contour. A single individual, having this feature of 

 the frontal limb in a marked degree, was found at Lagrange mountain ; 

 while two other individuals have been found at Stillwater, in the Lower 

 Magnesian limestone or Calciferous sandstone. 



These differences, of apparently minor importance, might not be regarded 

 as worthy of specific distinction ; but we have, at the same time, a difference 

 of form among the hypostomse. Whether these are all varieties of form of 

 one species, may admit of same 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 ix, fig. 11, is a small specimen (one side of which has been restored in the 

 figure) from Lagrange mountain. Minnesota. 



Plate x, 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 re- 

 maining, it appears as if separated along a suture line. 



