4.04. Prof. F. M‘Coy on the Classification of 
Trimerocephalus (M‘Coy). 
Etym. tpimepys, tripartitus, and xepary, 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, convergmg 
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 rimerocephalus. 
wider than the axis, bent down at their margin; each of the 
axal segments with a strong tubercle at each end; pleure 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 Miinster, 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 
(Paleozoic 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 levis of Miinster (Ca/lymene levis, Phil. Pal. Foss., 
not of Miinster, whose Calymene levis 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. 
Illenus latus (M‘Coy). 
Sp. Char. Cephalic shield more than twice as wide as long, mo- 
