236 .v.. MR. P. LAKE ON THE BRITISH [M&y 1896/ 



Oeratocephala goniata, and which helongs to the same group as 

 A. vesiculosa etc. Warder's name was rejected by Corda on the 

 ground that it had already been employed, in the form Cerato- 

 cephalus, for a genus of plants ; but even if it be eligible, its rival, 

 Acidaspis, has been so widely used for so long a time that, here at 

 least, I do not propose to adopt any other. 



II. Description of Species. 



Acidaspis Brighti, MurcH. (PI. 'VII. fig. 5.) 



1839. Acidaspis BrigMii, Murch. ' Sil. Syst.' p. 658, pi. xiv. fig. 15 ; 1848. Salter, 

 Mem. GeOl. Surv. vol. ii. pt. i. p. 348, pi. ix. figs. 6(?), 7 (not figs. 8, 9). 



(Not Odontopleura Brightii, Beyrich, ' TJnters. fiber Tril.' p. 20, pi. iii. fig. 6.) 



Head transverse, crescentic, with one occipital and two genal 

 prolongations or arms ; tuberculate. Glabella prominent ; central 

 portion nearly uniform in width throughout, but slightly contracted 

 between the second pair of lateral lobes ; lateral lobes two on each 

 side, almost completely separated from the central portion ; the 

 basal lobe much the larger of the two. Occipital ring very indi- 

 stinctly separated from the glabella, produced backward into a single, 

 strong, straight median spine. Eyes placed far back, and very 

 near to the basal lobe of the glabella ; connected with the front 

 end of the glabella by a nearly straight ocular ridge. Free cheeks 

 small, with a raised margin, which bears a number of spines directed 

 downward ; genal angles produced into long and strong spines, 

 which form a continuous curve with the posterior margin of the 

 head, but make a distinct angle with the external margin. 



Horizons and Localities. — Wenlock Limestone : Dudley. Lower 

 Ludlow : near the Wych, Malvern. It has been recorded from the 

 Bala beds, but this is probably due to mistaken identification. 



Affinities. — Only the head is known with certainty. It closely 

 resembles A. Grayi, Barr., but is distinguished, as Barrande has 

 pointed out, by the following characters: — (1) the genal spines in 

 A. Brighti are inclined to the axis at an angle of about 45°, while 

 in A. Grayi they are nearly at right angles to it ; (2) the occipital 

 spine in A. Brighti is usually somewhat smaller than in A. Grayi, 

 and does not bear the prominent tubercle characteristic of the latter ; 

 (3) the ocular ridge in A. Brighti is nearly straight, in A. Grayi 

 strongly arched ; (4) the granulation in A. Brighti is much coarser 

 and stronger than in A. Grayi. 



It is easily distinguished from all other British species by the 

 single strong occipital spine. 



Remarks on the Synonymy. — The species was originally described 

 and figured by Murchison, and formed the type of his genus 

 Acidaspis. In 1848 Salter gave a fuller account of the form ; but 

 unfortunately he confounded two species under the same name, and 

 figured two distinct heads and two distinct tails. One of the species 

 is identical, with Paradoxides quadrimucronatus, Murch., and hence 

 this name is usually quoted as a synonym of A. Brighti. Sub- 

 sequently Salter recognized his error, and, in 1857 he described the 



