FOSSILS OF THE LOWER SILURIAN. 97 
There are but slight traces of the fixed cheeks attached to the glabella. 
The species is characterized by the peculiarly shaped glabella. 
Formation and locality—Pogonip Group, on the west slope of McCoy’s 
Ridge, Eureka District, Nevada. 
Genus ILLA.NURUS Hall. 
TIilzenurus Eurekensis, n. sp. 
Plate xii, figs. 4, 4a. 
Head of medium width, semi-elliptical; glabella subquadrate, convex, 
a little longer than wide, as 5 to 4, with scarcely perceptible occipital or 
dorsal furrows; palpebral lobes nearly central on the margins; frontal mar- 
gin nearly straight; free cheeks a little longer than wide, with the base of 
the eyes cutting into them about the middle of the inner margin; genal 
angles broadly rounded. 
The facial suture, cutting the frontal rim on a line with the outer edge 
of the eyelobe, passes directly to the anterior margin of the eyelobe; it 
encircles that and then curves gently outward to the posterior margin, form- 
ing a short, triangular-shaped lateral limb. 
Surface minutely punctate. 
The pygidie associated with the head parts vary very much. Two 
are illustrated on plate xii, figs. 12 and 19, neither of which has any re- 
semblance to the pygidium of Illenurus. Another, discovered since the 
plate was prepared, shows a short, smooth axial lobe, slight dorsal furrows, 
and gently convex, broad lateral lobes; this is probably the pygidium of 
this species, as numerous examples of the glabella occur on the same frag- 
ment of rock. 
In the fourth volume of the Geology of Wisconsin a species of Ilex- 
nurus, J. convexus, is given as occurring in the Lower Magnesian limestone 
of that State, and the genus is also represented in the Potsdam sandstone, 
Illenurus quadratus Hall. In Nevada as yet it is only known from the 
horizon above that representing the Potsdam, or the correspondent of the 
Calciferous formation of the New York geologists. 
Formation and localities—Lower portion of the Pogonip Group, on the 
east slope of the ridge east of the Hamburg Ridge; on second ridge south- 
T7ODW 
