CRUSTACEA. 143 



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

 axal segments with a strong tubercle at each end ; pleurcR 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 

 (Palaeozoic 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 Miinster [Calymene Icevis, Phil. Pal. Foss., 

 not of Miinster, 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. 



Illanus latus (M'Coy). 



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

 derately gibbous towards the base, but about one-half of the 

 front arched over to a vertical position (or at right angles to 

 the basal portion or plane of the body) ; axal furrows consider- 

 ably less than half the length of the head, width of the in- 

 cluded space, or glabella, equal to two-thirds the length of the 

 head ; eyes small, near the lateral angles, their own length in 

 front of the posterior margin, two-thirds the width of the gla- 

 bella distant from the axal furrows. Length of head 10 lines, 

 width 1 inch 9 lines. 



This is only likely to be confounded with the /. crassicauda 

 (Dal.), from Gothland specimens of which it differs by the greater 

 width of the head and less depth of the deflected front, and most 

 remarkably by the very small size of the cheeks, resulting from 

 the eyes being removed almost to the lateral angles ; in the 

 /. crassicauda they are only half the width of the glabella distant 

 from the axal furrow, and the portion of the cheeks from the eye 

 to the lateral angle is nearly one- third more than from the eye 



