CANADIAN PERIOD. 59 



distance between them being equal to a little more than half the length of 

 the hinge-line. Eye-tubercle not detected. Surface apparently smooth. 



This species agrees nearly in size with, and bears a close general 

 resemblance to, L. Canadensis Jones, from the Calciferous sandstone foraia- 

 tion of Canada ; but it may be readily distinguished from that sjiecies by 

 the jDrominent angles at the ends of the hinge-line, the laterally-flattened 

 anterior and posterior borders, the greater convexity below the middle, and 

 by the presence of the two large pores at the ventral border of the right 

 valve. 



Position and locality. — Strata of the age of the Quebec group of Canada; 

 Queen Spring Hill, Scliell Creek range, Nevada. 



Collected by Mr. J. E. Clayton. 



Order TRILOBITA. 

 Family ASAPHIDiE. 



Genus MEGALASPIS Angelin, 1854 

 Megalaspis belemnurus White. 



Plate III, fig. 9. 



Megalaspis helemnurus ,W]iiie^ 1874, Exp. & Surv. west 100th Merid., Prelim. Rep. 

 Invert. Foss., 11. 



Pygidium subtriangular in outline, moderately convex transversely, 

 and only slightly convex along the median line; length compared with the 

 width across its anterior end about as fifteen to twenty- two; each outer 

 margin having a wide smooth border, the outline of which is only slightly 

 convex except near the antero-lateral angles, where the convexity increases 

 and the angles are abruptly rounded; anterior margin moderately convex; 

 posterior extremity ending in a short spine-like process; segmentation some- 

 what indistinct, but is most apparent upon the anterior portion of the axis; 

 trilobation also rather obscure; axis depressed, slightly higher than the 

 adjacent portions of the lateral lobes, its width equal to about one-half the 

 width of a lateral lobe, ending posteriorly in the elevated tenninal portion 

 of the pygidium; dorsal fun'ows moderately distinct upon the anterior half 

 of the pygidium but become obsolete posteriorly; lateral lobes slightly 



