86 



BRITISH CAMBRIAN TRTLOBITES. 



1865. OJenvs (Sphserophthalmus) pecten, Salter, Quart. Journ. Geol. Soc, vol. xxi, p. 481, figs. 4, 5. 

 1873. Olenus (Sphserophthalmus) pecten, Salter, Cat. Camb. Sil. Foss. Mus. Cambridge, p. 12, fig. 

 1880. Ctenopyge pecten, Linnarsson, Geol. Foren. Stockh. Forh., vol. v, p. 146, pi. vi, figs. 5 — 7, ? 9; 



not figs. 3, 4, 8. 

 1892. Ctenopyge pecten, Moberg, Geol. Foren. Stockh. Fork., vol. xiv, p. 351, figs. 1, 2. 



Head wide, emarginate in front, with genal spines springing from the middle 

 of the free cheeks. Glabella rather narrow, narrowing anteriorly, rounded in front, 

 reaching the marginal furrow, the anterior pair of glabellar furrows obsolete, the 

 posterior pair decidedly oblique, meeting across the middle ; neck-furrow well 

 defined, with a median tubercle. Byes large, oval, long axis inclined forwards and 

 outwards, placed near the middle of the cheeks; ocular ridge oblique. Facial 

 suture cutting the anterior margin very obliquely, running backwards and outwards 

 to the eye, and behind the eye bent abruptly outwards and backwards in a straight 

 line to the posterior margin, which it meets at an acute angle. Fixed cheeks at 

 the eye about equal in width to the glabella, behind the eye nearly twice that width ; 

 Free cheeks with a convex outer margin and a nearly straight posterior margin 

 meeting at a definite angle. Genal spines proceeding not from the genal angle but 

 from a point some distance above, directed outwards and backwards, the outer 

 edge being almost continuous with the outer edge of the cheek. 



Thorax consisting of eight or nine segments, considerably wider than the head, 

 attaining its greatest width about the fifth segment. Axis very narrow, less than 

 one sixth of the total width, each segment with a median tubercle. Pleura? lone: 

 and slender, straight, horizontal, terminating in slender spines; pleural grooves 

 narrow, running nearer to the anterior than to the posterior border, continued into 

 the base of the spines. 



Tail apparently consisting of six segments, similar to those of the thorax, fused 

 to a smaller terminal portion ; width about one and a half times the length. Axis 

 very narrow, about a quarter of the total width, with a ridge down the middle 

 which finally becomes free and is continued as a long straight spine directed 

 horizontally backwards ; the axis on each side of the ridge divided by six oblique 

 furrows. Lateral lobes showing six distinct pleurae fused together and retaining 

 all the characters of those of the thorax, each pleura ending in a long spine directed 

 backwards and sometimes inwards. Behind the last pleura is a small terminal 

 plate, emarginate behind. 



Dimensions.— The most complete specimen available (Plate IX, fig. 9) appears to 

 have had a length of about 9 mm. and a width of about 10 mm. ; and this seems to 

 have been rather below the usual size. Plate X, fig. 4 shows a part of a considerably 

 larger individual, and fragments of still larger ones are to be seen in the Oxford 

 University Museum. 



The thorax and tail can scarcely be confounded with those of any other 



