

Raymond & Narraway : Notes on Ordovician Trilobites 245 



Illaenus conradi Billings. 



(Plate LX, figures 9, 10.) 



Illcenus conradi Billings, 1859, Canadian Naturalist and Geologist, 



Vol. IV., p. 372. 

 Panderia conradiVodges, 1893, Occasional Papers California Academy 



of Sciences, No. 4, p. 330. 



We are able to add but little to Billings' elaborate description of this 

 species, but have introduced figures of this rare trilobite to show its 

 relation to Illcenus angusticollis. From that species it differs in the 

 greater width of the axial lobe and the glabella, the direction of the 

 dorsal furrows, and the less extended genal spines. On the axis of the 

 pygidium, annulations are suggested by faint lines or rows of punctae, 

 but the rings are not so definitely marked as in Illcenus angusticollis. 

 The first two thoracic segments are marked by two or three parallel 

 rows of punctae, while the other six segments usually show one row 

 each. 



Locality. — This species occurs in the Black River Limestone about 

 Ottawa, but perfect specimens are very rare. In several years of col- 

 lecting Mr. Narraway has found only ten entire specimens, four of 

 which were enrolled. These specimens have been obtained at Tet- 

 reauville and Mechanicsville, on opposite banks of the Ottawa River, 

 at La Petite Chaudiere, near Ottawa, Canada. 



Illaenus angusticollis Billings. 

 (Plate LXI, figures 1-5.) 

 Illamus angusticollis Billings, 1859, Canadian Naturalist and Geologist, 

 Vol. IV., p. 376, figs, \oa-\od. 



Only the cephalon of this species was known to Billings, but Mr. 

 Narraway has been fortunate enough to secure several entire specimens. 

 From this material the following description has been drawn up. 



Description. 



Body ovate, the greatest width exceeding the length. Dorsal furrows 

 deep, extending Upon both cephalon and pygidium. Length of an 

 average specimen, about 12 millimeters. 



Cephalon wide, the anterior margin gently arcuate, somewhat con- 

 tracted in front of the eyes, the free cheeks extended into short spines. 

 The dorsal furrows are deeply incised, outlining a narrow glabella. 



