96 DESCRIPTION OF A NEW TRILOBITE. 



Head — exclusive of spines, semi-circular, more than twice as 

 wide as long ; truncate in front, and prominently convex in the 

 middle, with a narrow equal border one half a line in width, 

 extended at the posterior angles with the free cheeks into mode- 

 rate diverging spines ; posterior margin marked by a shallow 

 furrow, reaching from the glabella outward to the free cheeks ; 

 eyes not large, smooth, and equi-distant from the front and pos- 

 terior margins, and about one line from the glabella ; the ocular 

 ridge prominent, extending from the eye obliquely forward to the 

 glabella, meeting the latter at about one line from the front thereof; 

 facial 'suture running obliquely from the eye, and cutting the 

 front and posterior margins far outward. The free cheeks are 

 not quite so smooth as the central lobe of head, but no radiation 

 or other marking is visible. 



Glabella — bell-shaped ; width less than one third of the 

 entire head ; broadly rounded in front, reaching nearly to the 



consented to allow me to publish a note on them in this place. The spe- 

 cies is unquestionably congeneric with those which I have called Dike- 

 locephalus Belli and D.Oweni from the same locality. My references 

 were founded on fragments of the head, consisting of detached glabellae, 

 but the aspect presented by these new specimens, (which exhibit all the 

 parts) is that of the genus Olenus. As the structure of the underside of 

 the head is unknown, it cannot yet be positively decided that this spe- 

 cies truly belongs to that genus, but it is the best reference that can at 

 present be made, and was Mr. Devine's first conclusion. There are two 

 points of difference that are worthy of notice. In Olenus (at least in all 

 the 21 species figured by Angelin), the facial sutures run from the eyes 

 either nearly straightforwards, or turn a little inwards. In this spe- 

 cies they curve outwards. This is their course in Dikelocephalus. The 

 eyes also in Olenus are, in general much more distant from the sides of 

 the glabella than they are in this species. Should the underside of the 

 head of the Swedish species of Olenus and of O. Logani turn out to be 

 the same in structure, then no one would hesitate to place them all in 

 the same genus. In Dikelocephalus Oweni the head is composed of three 

 pieces only : 1. — The glabella with the fixed cheeks. 2. — The hypostoma. 

 3, The two movable cheeks which are united together by a band ex- 

 tending across the front margin on the underside of the head. I think 

 it will turn out that 0. Logani is of the same structure. 



Angelin has described the Swedish species of Olenus under eight sub- 

 genera and Mr. Devine's species might form the type of a ninth, differ- 

 ing as much from them, as they do from each other. His discovery is an 

 important addition to our knowledge, as we now know (from entire spe- 

 cimens) that the genus Dikelocephalus, so characteristic of the base of 

 the palaeozoic rocks of America, is closely allied to the genus Olenus. 



