11 



converge in front of the eye, while in that one they are slightly diverg- 

 ent. We know of no other species with which it is closely related, 

 unless it should prove to be more nearly related to Agraulus Oiceni, 

 Meek & Hayden, Pal. Upp. Missouri, p. 9, figs. A, B, C, than we are 

 inclined to believe. There are several particulars in which it differs 

 very materially from their figures, and also from the description given, 

 that would at once mark it as distinct, if it were not that the imperfect 

 material in both cases tends to lead to error. The difference in the 

 width of the occipital lobe is a very marked one, and also the length of 

 the frontal limb, while the form of the glabella varies much in being 

 more distinctly conical than in that species. 



Formation and locality. In coarse sandstones of the Potsdam forma- 

 tion, at Castle Creek, West Black Hills, Dakota. 



CREPICEPHALUS (LOGANELLUS) PLAXUS, n. sp. 



Plate 2, fig. 20. 



Glabella and fixed cheeks, when united, subquadrangular in outline, 

 narrowest across the eyes and slightly expanding in front, and more 

 abruptly so posteriorly. Glabella very depressed convex, slightly 

 conical and somewhat squarely truncate in front, the width across the 

 base being equal to about three-fourths of the height above the occipital 

 furrow, and that of the anterior end to about half the height j lateral 

 furrows very faintly marked, oblique, and extending about one-third of 

 the width from the margin. Occipital furrows not strongly marked, 

 extending entirely across the base of the head ; ring narrow, and with- 

 out spine. Dorsal furrows distinct, but not deep, extending around 

 the front of the glabella. Fixed cheeks wide, more than half as wide, 

 opposite the eyes, as the middle of the glabella. Frontal limb of moder- 

 ate length, at least as long as the width of the anterior end of the gla- 

 bella, but its entire extent and anterior margin have not been fully ascer- 

 tained. Facial suture cutting the anterior border at right angles to the 

 margin of the head and directed slightly inward to the eyes, behind which 

 it is directed obliquely backward, at an angle of about 60 with the base 

 of the head, to the occipital furrow, behind which it runs more directly 

 outward. Ocular ridges distinct. Palpebral lobes small and situated 

 behind the middle of the head. 



The species is only known by the glabella and fixed cheeks, and is 

 remarkable only for its general flatness and want of prominent charac- 

 ters. There is no known species from the same formation either in the 

 Wisconsin locality or from the more western regions that is so closely 

 related to it as to be readily mistaken. <?. (L.) quadra-vis, H. & W., 

 of Clarence King's report, from the slates above Call's Fort, North 

 Wahsatach Mountains, is perhaps as closely related as any, but differs 

 in having the glabella more rounded in front and proportionally broader. 



Formation and locality. Associated in the same beds and locality 

 with the preceding species. 



