PRIMORDIAL PERIOD. 



Olenellus Howelli Meek. 



Plate II, fig. 4 a and T>. 



Olenellus Howelli Meek, 1874 (manuscript). 



Olenellus Howelli White, 1874, Geog. & Geol. Exp. & Surv. west lOOth Merid., Prelim. 

 Rep. Invert. Foss., 8. 



Head massive, semi-oval in outline, strongly convex, the length on the 

 median line being to the greatest breadth abont as three to five ; exterior 

 margin having a strong, raised border, of nearly uniform width all around, 

 and which is also continuous with the moderately strong spines of the 

 postero-lateral angles of the head ; length of the spines about equal to one- 

 half the length of the head on the median line ; posterior margin also 

 having a raised border extending on each side from the occipital segment 

 to the base of the spines, but not crossing the glabella upon the occipital 

 lobe ; width of this border not uniform like that of the exterior margin, 

 but is widest a little beyond the midlength at each side, and narrowest near 

 the base of each spine, toward which it again suddenly widens, blending 

 with both the spine and the exterior raised border ; this widening of the 

 border there rounds the angle -between the posterior margin and the spjne, 

 and also rounds the postero-lateral angle of that portion of the cheek which 

 is inclosed within the raised borders. A shallow, linear depression extends 

 around the head just within the raised border, giving the broad cheek- 

 surfaces the appearance of being slightly inflated. 



Eyes large, very prominent, extending from opposite the anterior 

 furrow of the glabella to nearly opposite the middle of the occipital lobe ; 

 the palpebral lobe of each eye blending with the outer ends of the anterioi', 

 middle, and posterior lobes of the glabella. 



Glabella large, very prominent, distinctly lobed ; the furrows, while 

 they are, distinct at the sides, are only slightly impressed at the median 

 line ; occipital and posterior lobes of about equal size ; frontal lobe large, 

 tumid, well defined, extending forward to the shallow, linear depression 

 just within the raised border of the anterior margin of the head, regularly 

 rounded in front, a little wider than the remainder of the glabella, but not 

 higher than the others of its lobes. 



