PRIMORDIiVL FOSSILS. 343 



the widtli 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.. 



FormatioH and locality. — In coarse sandstones of the Potsdam formation, 

 at Castle Creek, Black Hills, Dakota. 



CREPICEPHALUS PLANUS. 



Plato 2, fig. 20. 



Crepicephalus (Loganellus) planus Whitf., Prelim. Kept. Pal. Black Hills, 1877, p. 11. 



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

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

 abruptly so posteriorly. Glabella very depressed convex, slightly conical 

 and somewhat squai'ely 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 equal to about half the height; 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 without spine. Dorsal furrows 

 distinct, but not deep, extending around the front of the glabella. Fixed 

 cheek wide, more than half as wide opposite the eye as at the middle of the 

 glabella. Frontal limb of moderate length, at least as long as the width of 

 the anterior end of the glabella, but its entire extent and anterior margin 

 Las not been fully ascertained. 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 characters. 

 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. 6. {L.) quadrans H. & W., Geological Ex])loration 



