Vol. 52.] FAUNA OF THE KEISLEY LIMESTONE. 425 



It is, however, impossible to express a decided opinion until we find 

 indubitable evidence that some of the so-called Sjrfi. mirus-heada of 

 the Keisley Limestone belong to the new species latirugatus. 



It is noteworthy in this connexion that only one typical Sph. 

 mirus-py gid'mm has been found at Keisley, whereas fragments of 

 the Sph. latirugatus-ipygi&ium are not very uncommon. 



raillim. 



Length of pygidium 8 



Breadth „ 15 



Some other less perfect specimens must have been longer in 

 proportion to their breadth. 



Note. — Salter (Geol. Surv. dec. vii. 1853, pi. iii. fig. 15) figures a 

 tail of this new species from Kildare, but includes it with Sph. 

 mirus, though with the remark that it is ' more elongated than 

 in the Dudley specimens.' I have seen several specimens from 

 Kildare agreeing with the above description. 



Stattrocephalus ITtjrchtsoni, Barr. 



This genus has not previously been recorded from the Keisley 

 Limestone, but I was fortunate enough to obtain more than half a 

 dozen specimens of the head-shield during a recent visit. They 

 occurred in the same blocks with many of the characteristic Keisley 

 Limestone fossils, so that no doubt can be entertained that they 

 belong to this horizon. 



Their identification with Barrande's species is rendered specially 

 easy, since in the Woodwardian Museum is ahead of Stauroeephalas 

 from Ehiwlas (figured by M'Coy) which Barrande himself examined 

 and held was indistinguishable from his Bohemian species. 1 Our 

 Keisley specimens show all the typical features, though unluckily 

 the free cheeks are not preserved. The position of the eye at once 

 distinguishes this species from St. ylobiceps (Portl.), figured and 

 described carefully by Salter. 2 



Acidaspid^:. 



Acidaspis convexa, sp. n. (PI. XXI. fig. 6.) 



The genus Acidaspis has not previously been recorded from the 

 Keisley Limestone, but I have recently found two fairly good head- 

 shields presenting characters which prove that the}^ belong to this 

 genus, and to a new species. 



The head-shield of this new form is very convex from back to 

 front, and also, but to a less extent, from side to side. The glabella 

 shows a median convex portion of cylindrical shape, with parallel 

 sides and more than twice as long as wide. This central portion of 

 the glabella forms the crest of the head-shield, and its apex is nearer 

 the front than the hind border. The anterior end is lofty, steep, 

 and abrupt, but the posterior end slopes more gradually down to the 



1 It is mentioned by Barrande in ' Syst. Sil. Boheme,' toI. i. (1852) p. 812, 

 pi. xliii. fig 28. 



2 Mem. Geol. Surv. dec. xi. (1864) pi. v. fig. 6, p. 3. 



2g2 



