242 MR. P. LAKE ON THE BRITISH [May 1 896, 



ever to have been published. Unfortunately, in 1854, Angelin 

 adopted the name A. Barrandei for a species quite distinct from 

 this, and allied to A. crenata. As, however, Fletcher's name had 

 already been published and applied to a definite figure, it would 

 appear to have priority. 



Acidaspis Hughesi, Salter MS. (PI. VIII. figs. 4 & 5.) 



1873. Acidaspis Hughesii, Salter, ' Cat. Cambr. & Sil. Foss.' p. 93. 



General form depressed, broadly ovate. 



The head forms a transverse semi-oval. The glabella consists of a 

 parallel-sided median portion and two lateral lobes on each side, 

 completely cut off from the median portion ; the basal lobe is much 

 the larger. The facial suture cms the posterior margin just within 

 the genal spine. Eyes small, set somewhat far back. Fixed cheeks 

 narrow, tumid. Free cheek broad, granulate, provided with a raised 

 margin bearing a row of spines, which become longer towards the 

 genal angle ; genal angle produced into a short weak spine directed 

 backward and outward. The axis of the neck-segment bears two 

 short spines, which are seldom visible. 



The thorax consists of nine segments, and is of nearly equal width 

 throughout. Axis narrow, about one fourth the total width of the 

 body. Pleuraa straight ; the greater part of each is occupied by a 

 broad prominent ridge, which bears a row of some half-dozen 

 tubercles ; on each side of this main ridge is a very narrow band, 

 the anterior one being somewhat the broader, slightly raised and 

 finely tuberculate. Both the central and the anterior ridges are 

 produced into spines, those from the former being considerably the 

 longer. These spines curve backward and increase in length 

 towards the posterior end of the body. 



Tail broad, granulate. The axis consists of two rings and a 

 terminal knob, the second ring being often very indistinct. The 

 margin bears a row of radiating spines, namely : — 2 larger spines 

 connected with the axis by a rib ; 4 smaller ones between these ; 

 and 4, or perhaps 5, outside each of the larger spines. 



Horizons and Localities. — In the Jermyn Street Museum there are 

 specimens of this species from Brownthwaite, Gale Garth, Casterton 

 Low Fell, and Kavenstone Dale. The last three localities are referred 

 to the Upper Coldwell Beds by Mr. Marr, 1 who also records the species 

 from the same beds at Helm Knot. In the Woodwardian Museum 

 there are specimens collected by Prof. Hughes from beds above the 

 INant GJyn Flags at Pont Lawnt in Denbighshire, which he believes 

 to be on the same horizon as the beds of Casterton Low Fell. 2 



The specimen on which Salter is stated to have founded the 

 species was brought from Casterton Low Fell, and is now in the 

 Woodwardian Museum. 



In the Jermyn Street Museum there is a specimen of Acidaspis 

 which is stated to come from the Llandeilo Flags near Pencerrig 



1 Geol. Mag. 1892, p. 538. 



2 Proc. Chester Soc. Nat. Sci. & Lit. pt. iv. 1893, p. 154. 



