Vol. 52.] SILURIAN SPECIES OF ACIDASPIS. 241 



Museum, referred to in Salter's ' Catalogue,' that the name is 

 applied to the species here described. 



Acidaspis Barrandei, Fletcher & Salter, non Angelin. (PI. VIII. 

 figs. 1-3.) 



1848. Acidaspis bispinosus, Salter, Mem. Geol. Surv. vol. ii. pt. i. pi. ix. fig. 4 

 (only). 



1853. Acidaspis Barrandii, Fletcher (dixit Salter), Mem. Geol. Surv. dec. vii. 

 p. 6, pi. vi. ; 1854. Fletcher & Salter, in Morris's ' Catalogue of Brit. Fossils,' 2nd ed. 

 p. 98 ; 1859. Murchison, ' Siluria/ 3rd ed. p. 261, Foss. 64, fig. 9. 



General form quadrate, nearly as wide behind as in front. 



Head quadrate, widest in front, tuberculate. Axal furrows almost 

 obsolete ; median portion of glabella swollen, narrows slightly 

 towards the front ; two pairs of lateral furrows deeply impressed ; 

 lateral lobes very indistinctly separated from the cheeks. Facial 

 suture invisible. Eye small, prominent, set in the middle of the 

 cheeks ; ocular ridge straight. Fixed cheeks large and tumid. The 

 free cheeks widen out towards the front, with a broad tuberculate 

 raised margin bearing a row of short spines. Moderately long 

 slender spines at the genal angles, but these do not appear to spring 

 from the margin. The axal part of the occipital ring is produced 

 into a pair of spines directed backward and outward. 



The thorax consists of ten segments. Axis wide ; each segment 

 bears two prominent tubercles. Pleurae broad, flat, tuberculate ; 

 at a distance from the axis about equal to the width of the axis, all 

 but the last are abruptly bent downward and produced into a short 

 ornamented spine (very rarely visible) ; and from the angle of the 

 bend long horizontal spines are given off. The horizontal spines 

 are arranged in a radiate fashion, those from the anterior segments 

 being directed slightly forward, and those from the posterior 

 segments backward. The last segment differs from these, and 

 bears two ornamented horizontal spines on each side. 



Tail broad, tuberculate ; axis ill-defined. The margin bears five 

 longer spines, one being median, and from the front of the base of 

 each lateral spine is given off a smaller ornamented spine, thus 

 making a total of nine. 



Horizon and Locality. — Wenlock Limestone : Dudley, Callow 

 Farm. 



Affinities. — A. Barrandei is closely allied to A. Yerneuili, Barr., 

 and A. vesiculosa, Beyr., and in fact is chiefly distinguished by the 

 characters of its tail. A. vesiculosa has five spines to its tail, 

 A. Vemeuili seven, and A. Barrandei nine. 



A. bicuspis, Ang., belongs to the same group. Only one specimen, 

 which is now in the Biksmuseum at Stockholm, appears to have 

 been found, and it is scarcely perfect enough to allow of one's 

 asserting with confidence whether it is a distinct species or not. 



Synonymy. — The head of this species was originally figured by 

 Salter in 1848 under the name A. bispinosus. In 1853 he corrected 

 his mistake, and stated that the form had been named A. Barrandii 

 by Fletcher, and would shortly be described. Since then this name 

 has been in common use in England; but no description seems 



