404 Prof. F. M'Coy on the Classification of 



Trimerocephalus (M'Coy). 

 Etym. TpL/iepr)?, tripartitus, and tcefaCky, caput. 



Gen. Char. Elongate ovate : cephalic shield semicircular, with the 

 lateral angles obtusely rounded : glabella very broad, gently 

 convex, widely rounded and touching the 

 margin in front; sides straight, converging 

 to the narrow base ; neck-furrow strong, and 

 one fine, directly transverse, segmental furrow 

 a little above it across the base of the glabella ; 

 cheeks smaller than the glabella, triangular, 

 evenly convex, without eyes or facial sutures ; 

 limb almost wanting in front of the glabella, 

 forming a narrow margin to the cheeks, and 

 being rounded at the lateral angles forms the 

 thick posterior margin of the shield and neck- 

 segment ; thorax of eleven joints, lateral lobes Trimerocephalus. 

 wider than the axis, bent down at their margin ; each of the 

 axal segments with a strong tubercle at each end ; pleurae, of 

 equal width throughout, blunt at their ends, which are bent 

 downwards and a little backwards, each marked along the 

 middle by a pleural groove, angularly bent backwards about 

 the middle, but not reaching the margin ; trigonal facets small, 

 narrow ; pygidium small, obtusely rounded, entire, axal lobe 

 distinctly rounded with about four or five segmental furrows ; 

 lateral lobes with about five flattened segments, each divided 

 by a furrow. 



This genus has been confounded by Count Munster, in his 

 'Beitrage zur Petrefactenkunde ' for 1842 (only knowing the 

 head), with Trinucleus, from which the structure of the body and 

 tail, as well as the absence of the punctured border of the head, 

 remove it very far; and it has been referred by Prof. Phillips 

 (Palseozoic Fossils) to Calymene, from which the form of its ce- 

 phalic shield and glabella, want of eyes and facial suture, and 

 the different number of the body-segments, will I think suffi- 

 ciently distinguish it. 



I only know the genus in the Devonian rocks, the type being 

 the Trinucleus Icevis of Munster (Calymene Icevis, Phil. Pal. Foss., 

 not of Munster, whose Calymene Icevis is a true Portlockia, M'Coy). 

 It is perhaps most allied to Ellipsocephalus of Zenker, which has 

 however twelve body-rings, eyes at the sides of the cheeks, a 

 glabella pointed in front, and a little pygidium without segmental 

 furrows. 



Illcenus latus (M'Coy). 



Sp. Char. Cephalic shield more than twice as wide as long, mo- 



