Raymond : Notes on Ordoviciax Triloiutes. 69 



Subfamily OCrVGIXyE nov. 



Genus XiLEUS Dalnian. 



Nileus perkinsi sp. nov. 



Plate XVIII, figures 7, 8. 



This species is so far known from only two specimens, one collected by 



Professor Perkins on Isle La Motte, and the other a specimen from the 



same localil>' in the U. S. National Museum. 



Description. 



Cephalon about three-fourths as long as wide, strongly and evenly 

 convex, sloping gently to the sides without any depressed border. Eyes 

 very large, situated far apart and close to the posterior border of the cepha- 

 lon. The glabella is not differentiated from the remainder of the cephalon, 

 and is smooth except for a very small median tubercle. The genal angles 

 are not well preserved on either of the specimens at hand, but appear to 

 be regularly rounded and aspinose. The surface of the test is marked by 

 very minute punctae. 



Of the thorax only five segments are preserved. It is strongly convex 

 and dorsal furrows appear to be absent. The pygidium is as yet 

 unknown. 



This species differs from Nileus vigilans (Meek and Worthen) as de- 

 scribed by Clarke from Minnesota in several particulars, but principally 

 in respect to the eyes, which are much larger and farther back in our 

 species. The species from the Chazy is much more closely allied to Nileus 

 scrutator Billings, but differs from that species in having the cephalon 

 longer in proportion to the width. One of the cephalons of Nileus 

 perkinsi is 25 mm. long and 35 mm. wide, while Billings gives the measure- 

 ments of one of his specimens as 9 lines long and 17 lines wide. According 

 to Billings' figure the anterior portion of the cephalon of N. scrutator is 

 abruptly incurved, while the axial portion of the cephalon of the species 

 here described is almost flat. Both Nileus macrops Billings and N. affinis 

 Billings have eyes much larger and placed further forward than in our 

 species.' 



Locality. — Both specimens are from the buff dolomite at the base of 

 the upper Chazy on Isle La Motte, Vermont. The species is named for 

 Professor George H. Perkins, the eminent State Geologist of Vermont. 



'Paleozoic Fossils of Canada, Vol. I, pp. 273-275, figs. 259-261, and Pale- 

 ontology of Minnesota, Vol. Ill, pt. II, p. 712, figs. 17-19. 



