IN THE UPPEE GEEEN SLATES OF NOETH WALES. 77 



Tremadoc Slates, the two most abundant forms, Conoeoryphe * (with 

 19 species) and Olenus (with 15 species), possess many characters bj^ 

 which they approach one another and also the Penrhyn Trilobite. 

 The forms of Agnostus, of which 12 have been described from these 

 Cambrian rocks, may be dismissed here as outside the present 

 inquiry. 



In Paradoxides the glabella is too much produced and globular in 

 front, and the body-segments and the axis taper gradually to the 

 pygidium ; there are not fewer than about 20 segments to the body. 



In AsapJius, Ogygia, and JViobe there are only 8 thoracic rings ; 

 but the caudal shield is very large, and the entire form is very 

 broadly oval. 



Angelina agrees with our Penrhyn fossil very well in size, and in 

 the number of its free thoracic segments, but its glabella is quite 

 smooth, and the pleurae are broader, and its cheek-spines are very 

 long. 



Olenus has 14 free body-rings, the glabella is furrowed, but the 

 head-shield is shorter and broader, and the ends of the pleurae 

 and margin of the caudal shield are usually more produced into 

 spines than is the case in our fossil, and the Oleni are generally 

 of much smaller size. 



ConocorypTie^ Corda, 1847 (= Gonocephalites^ Barr., 1852), has 14 

 free segments, the axis (as in the Bangor specimen) is parallel -sided, 

 and does not diminish from the head backwards to the pygidium ; 

 each ring of the axis is notched on its posterior border ; the ends of 

 the pleurae are rounded ; the glabella is furrowed obliquely on each 

 side ; the eyes are sometimes wanting, but when present are small, 

 and are commonly placed in the axial furrow, near the latero-ante- 

 rior border of the glabella. Cheek-spines are sometimes absent, 

 and when present are never very long. 



From these considerations I conclude to place the Penrhyn Trilo- 

 bite in the genus ConocorypJie, and I have ventured to dedicate the 

 species to Mrs. Dobbie, under the name of ConocorypJie Viola. 



It is certainly distinct from any of the 19 species already described 

 from the Cambrian rocks of Wales or from other localities. 



Those who desire to consult the memoirs which have appeared on 

 the Trilobites of this area are referred to the following papers : — 



J. W. Salter, 1863. Quart. Journ. Geol. Soc. vol. xix. p. 274. 

 J. W. Salter, 1864. Mem. Geol. Surv. dec. xi. (Trilobites) chiefly 



Silurian. 

 J. W. Salter, 1864. Quart. Journ. Geol. Soc. vol. xx. p. 233, 



pi. 13. 



* Conocephalus was the name originally proposed by Zenker for certain 

 Trilobites, but it was found to have been already used by LatreiDe for a genus 

 of Insects. In 1847, Corda proposed to substitute the name Conocoryphe for 

 the first-described form of Conocephalus of Zenker, and the other species he 

 placed under the genera Pz^ycAo^arza and Ctenocephahos. Barrande later (1852) 

 proposed to retain Conocephalus by simply altering the termination to Cono- 

 cephalites ; but this course is not consistent with the prevalent rules of nomen- 

 clatvire, and Corda's name Conocoryphe should be adopted, even if the other 

 two genera proposed by him are not maintained. 



