80 BRITISH CAMBRIAN TRILOBITES. 



In any case the available evidence is not sufficient to justify us in assuming that 

 the species with broad fixed cheeks had tails like that of Gt. pecten, and if the 

 special character of the genus is to be a tail of this type, the generic position of 

 the greater number of species must remain doubtful. Provisionally, therefore, I 

 adopt Brogger's definition, basing the genus primarily upon the wide fixed cheeks 

 and neglecting the tail. In practice this was also what Linnarsson did in the case 

 of species other than Ctenopyge pecten. At the same time it is by no means improb- 

 able that when our knowledge of these forms is more extensive it may be found that 

 the large-tailed species really do constitute a distinct group, and if so it is to these 

 that the name Cteuopyije should be limited. 



The following characters will serve to distinguish the genus from the allied 

 forms. General shape depressed. Head wide, straight or emarginate in front. 

 Glabella nearly parallel-sided or slightly tapering forwards ; number of glabellar 

 furrows variable. Eyes large, not so far back as in Sphserophthalmus, with an 

 ocular ridge running towards the front of the glabella. Fixed cheeks wide or 

 fairly wide, considerably expanded behind the eye. Free cheeks with a long spine 

 springing abruptly from the middle of the external margin. Thorax usually with 

 nine or ten segments, pleurae produced into long spines which in the hinder 

 segments are bent strono-ly backwards. 



1. Ctenopyge fusiform! s, sp. nov. Plate VIII, fig. 14. 



Head wide, strongly emarginate in front. Glabella at the neck-furrow forming 

 less than one-third the total width of the cranidium, straight-sided, narrowing 

 considerably forwards, truncate in front, reaching the marginal furrow. Glabellar 

 furrows indistinct or absent, neck-furrow well defined. Eyes placed about half-way 

 between the anterior and posterior margins and at a distance from the glabella 

 rather less than the width of the latter ; an oblique ocular ridge running towards 

 the front end of the glabella. Facial suture running obliquely outwards from the 

 anterior margin to the eye, and from the eye obliquely outwards to the posterior 

 margin. Fixed cheeks at the eye rather less than the glabella in width, expanding 

 considerably behind the eye, where the width is about one and a quarter times that 

 of the neck-ring. 



Thorax of eight more segments. Axis forming about one-third of the 

 total width, widest about the third segment, with doubtful traces of median 

 tubercles. Pleurae nearly horizontal and almost straight, but in the first two 

 segments bent slightly downwards and backwards at the extremities, ending, 

 apparently, in short points ; pleural grooves broad and deep. 



Tail unknown. 



