CHEIRURUS. 75 



radiatis, lobo antico parvo trigono. Gena scrobiculata ncc scripts, longispinosce . Oculi 

 omnino antici,parvi. Thorax axe modico, fere ut pleuraslato, his convexis rectis, profunde 

 sulcatis, apicibus recurvis 4, longispinosis. Cauda major, axe 4<-(vel.- 7 ?)annulato, longo, 

 limbo sulcato et in spinas 6 retrorsum flexas subparattelas productis. 



This Trilobite, found about five years since by Messrs. Homfray and Ash, in the slates 

 of Portmadoc, is a member of a group more characteristic of higher beds. There cannot 

 be much doubt of the genus, and though the long spinous hinder pleura? are a new 

 character for this section of Cheirurus, it can only be compared with such species as the 

 Ch. (Eccopt.) claviger, before mentioned, and the E. Sedgwicki. Prom both, the spines — 

 and the deeply grooved, not punctate, pleurae — distinguish it easily ; I am not quite sure if 

 fig. 21 belongs to this or to a distinct species ; it is much larger, and has more joints 

 in the tail. 



Occasionally as much as three and a half inches long, and rather wide (all our speci- 

 mens are much compressed). The head is wide, less than semicircular; the outer cheeks, 

 occupying the greater part of the head, are margined all round by a continuous furrow, 

 and produced into long head-spines ; the border smooth. The eye is very far forward, 

 as in E. Sedgiciclci, and the facial suture so forward as to cut the outer margin much in 

 advance of the middle of the head, separating a very small free cheek. 



The glabella is not nearly so wide as the cheeks ; it is parallel-sided, apparently not 

 much longer than broad, and has the furrows very distinctly marked. These are three on 

 each side, and rather deep, all straight and inclined a little upwards, the front ones 

 especially, so as to have a radiate appearance. They reach more than one third across the 

 glabella, and thus leave but a narrow space down the centre. The front lobe, marked 

 out by the two converging front furrows, is a wide triangle, and does not occupy more 

 than a third of the length of the glabella, the surface of which is granulated. 



Thorax apparently of only eleven flattened rings, of which the axis is not quite so 

 wide as the pleurae ; these last are convex and deeply grooved along the middle, almost 

 to the ends ; each is produced into a long, sharp spine, bent backward in all the 

 segments ; but in the four or five hinder ones the spines are fully equal to the length of 

 the pleurae themselves. 



The tail, which can hardly be distinguished from the thorax, has in the more perfect 

 specimen (fig. 18), only four joints and a terminal piece to the axis. In fig. 21 there are 

 six or seven rings. The smaller specimen has the tail-spines more lateral. In the larger 

 one they reach more toward the end of the tail ; but part of this difference may be due 

 to pressure. 



C. Eryx, a species described by Mr. Billings from the Quebec limestones,* has a 

 larger number of tail-spines ; but it is a closely allied form. 



Locality. Upper Tremadoc slates ; Garth Hill, and Penclogwyn, Portmadoc (D. 



* In the 'Canadian Naturalist and Geologist,' vol. v, p. 322. 



