﻿102 



SILURIAN TRILOBITES. 



We formerly only knew the bead of this curious species (see fig. 25). It is 16 

 lines wide, and only 7 lines long. And of this length the tumid and produced front 

 is two thirds as long as the small parabolic glabella. The latter is very little convex, 



a good deal wider than long, truncate in front, 

 and with the three lateral lobes all distinct, ob- 

 lique forwards, and reaching well into the gla- 

 bella, especially the basal ones, which are subtri- 

 angular and much contracted at their inner edge. 

 The cheeks are large and tumid, and the small eyes 

 are placed far forwards, on a level with the upper 

 glabella-lobe, about as remote from it as the 

 width of the glabella. The neck- furrow is strong 

 C. parvifrons, nat. size and magnified. beneath the glabella, but broad and shallow under- 

 neath the capacious cheeks, and the lower margin of the latter is much curved. 



Prof. M'Coy's figure is very inaccurate in proportion. I have only lately been able 

 to see the specimen, and give a more correct outline in our woodcut than fig. 25 in 

 the plate, which was unfortunately copied from the Cambridge Synopsis. 



Var. Murchisoni. PI. IX, figs. 26—28. — Glabella latiori, oculis vix remotis. 



Imperfect as our materials are, it is clear this variety must be distinguished from the 

 typical C. parvifrons. The var. Murchisoni has a broader glabella, and the eyes less 

 remote, and larger. Such differences may be due to sex rather than variety, and there 

 is reason to suspect sexual variations to a small amount in this genus, as I have above 

 shown (p. 101). 1 This variety, MurcJdsoni, is much more like C. Tristani, from which, 

 indeed, except by the more truncate and less triangular form of the glabella, and far 

 less strongly ribbed tail, it is somewhat difficult to separate it. 



Locality. — Arenig or " Skiddaw " group. Tai hirion, on the road from Bala to 

 Ffestiniog; collected in 1844, by Prof. Sedgwick and J. W. Salter (Woodw. Mus.). 



Of the var. Murchisoni ; — the Stiper Stones ; viz. at Lord's Hill, and other neighbouring 

 localities. Also at Cae Glyd, under the Manod Bach, near Ffestiniog — and at Ty-obry, 

 near Garth, Portmadoc (Mus. P. Geology; and the cabinets of Messrs. Ash and 

 Homfray). 



1 Prof. Thomson, who has observed hundreds of specimens of the Calymene Blumenbaehii, thinks there 

 is no difference of sex observable in that species. But that is no reason for doubting it in others. 



