Ravmond-Narrawav : Notks on Ordovician Trilohites. 47 



'I'his wi'll -known si)ccics is \-cry ahiiiul.ml in the huff (loioniitc of the 

 Lu\v\illo at Mcchanics\illc, I\'l ton's (juarry and oilier jilaccs near Ottawa. 

 At some localities this is the onl>' trilobitc found in certain layers of the 

 Lowvillc. In one layer at I\Icchanics\ille where this is true, a few de- 

 tached hypostomas ha\e Iiccn found. Two of them are figured on the 

 plates which accompany this article. In his original description of the 

 genus Billings described the hypostoma as "oblong, not forked, somewhat 

 oval, an elexated margin around the posterior two-thirds in some species, 

 muscular impressions two, transverse or oblique, situated behind the mid- 

 dle." He did not give a figure, but in the "Paleozoic Fossils of Canada," 

 Volume I, page 408, he states that the hypostoma is exactly like that of 

 Ogygia The hypostomas here figured are certainly similar to that of 

 Ogygia, but they do n t answer well to Billings' description. However, 

 as Bathynnis extans is very ai)undant in the layer from which these 

 specimens were obtained, and is the only trilobite present, it is believed 

 that they belong to that species. 



The glabella of this species is strongly convex, and is outlined by deep 

 dorsal furrows and a very narrow concave anterior border There are 

 two pairs of shallow glabellar furrows, and in well preserved specimens the 

 test shows a \-ery few fine pustules scattered over the surface, as well as 

 numerous, fine, wavy striae. The neck-ring bears a low median pustule. 

 The eyes are large and situated near the neck-ring. The free cheeks 

 have narrow concave borders and the genal angles are drawn out into 

 long spines. 



The thorax has nine segments, is strongly convex, the axial lobe narrow, 

 the pleura flat on top and sloping gently at the sides. 



The pygidium is very convex, roughly triangular, and about three- 

 fourths as long as wide. The axial lobe has two rings and a trace of a 

 third on its anterior end Otherwise it is smooth. The pleura slope 

 rather abruptly to the narrow concave border, and show four pairs of 

 broad segments, the fourth pair not well defined. On the first two pairs 

 are slightly impressed lines. 



This species does not seem to occur in the Black River, being replaced 

 in that formation by Bathyuriis longispinus and B. spiniger. 



Bathyurus longispinus W'alcott. 



Plate XVI, figures 12-14. 



Bathyurus longispinus Wai.cott, Twenty-eighth Annual Report New York State 



Museum, 1879, 94. 

 fPtychopyge jerseyensis Weller, Paleontology New Jersey, III, 1902, 193, pi. 14, 

 fig. 16. 



