TRILOBITA—OPISTHOPARIA. 299 



Black River of Ontario; Trenton of Illinois, Iowa, Wisconsin 

 and Minnesota. 



XLV. NiLEUs Dalman. 



Very similar to Bumastus, but the eyes are larger, crescent- 

 shaped, and placed farther forward; the cephalon is more de- 

 pressed. Posteriorly the facial sutures extend obliquely outward 

 and backward from the eyes to within the broadly rounded genal 

 angle ; anteriorly they first curve outward and then converge nearly 

 parallel with and almost reaching the anterior margin.- Thorax 

 indistinctly trilobate and composed of eight very broad segments. 

 Ordovicic. 



111. N. vigilans Meek and Worthen. (Fig. 1610, c, J.) Ordovicic. 

 Eyes elevated, curved to form three fourths of a circle. 



Black River-Lorraine of Illinois and Minnesota. 



XLVI. Proetus Steininger. 



Cephalon semicircular, the thickened margin bounded inwardly 

 by a marginal furow. Glabella very convex, extending nearly to 

 the anterior margin of the cephalon, and rounded anteriorly; 

 occipital lobes usually present. Glabellar furrows often quite ob- 

 solete externally but sometimes with their position indicated by 

 dark lines on the surface which seem to show an internal thicken- 

 mg of the test. Neck furrow well marked. Eyes prominent, 

 smooth, and close to the glabella. Palpebral lobes lower than the 

 glabella. Facial sutures extending inward from the posterior mar- 

 gin inside the genal angle to the eyes and then forwards, cutting 

 the anterior margin separately. Thoracic segments usually ten, 

 convex, the pleura medially grooved by oblique furrows. Pygid- 

 ium semicircular, bounded by a flattened margin; its axis very 

 convex and not reaching the tip, and with usually less than 14 

 annulations. Entire surface of test granulose. Ordovicic- 

 Carbonic. 



112. P. pachydermatus Barrett. Siluric. 

 Glabella subtriangular, tapering forward, with a pair of ovoid, 



disconnected, basal lobes ; the two anterior pairs of furrows faint, 

 the third, just anterior to the ovoid basal lobes, is prominent, 



