185/.] SALTER ACIDASPIS. 211 



The head is semilunar, an inch wide, the front margin much 

 arched, its outer angles scarcely at all quadrate, and with about 

 eleven or twelve notches or short spines. The glabella is an equila- 

 teral triangle, very prominent, narrowly obovate, and not at all fused 

 with the cheeks ; the basal lobes large and circumscribed, the second 

 pair rounded, the uppermost (as in all this section of the genus) 

 wanting. 



The ocular ridges are narrow and distinct, diverging at an angle 

 of about 90°, and the intermediate lobe (between these and the gla- 

 bella) narrow, very prominent below, but not quite so broad as the 

 basal glabella-lobe. Eye small, placed far back, as in A. Brightii. 

 The posterior angles of the head are narrowed gradually into the 

 spine, which is oblique and continuous in direction with them, not 

 abruptly turned outwards. 



The tail much resembles that of A. Brightii and other species, in 

 which the primary spines do not differ greatly in size from the rest. 

 They are directed exactly backwards, or even converge a little ; there 

 are four terminal equidistant spines between them, and one outside 

 each. The axis is short, and the general shape of the tail shorter 

 and wider than in any of the other British Upper Silurian species. 



This character, taken with the produced and gradually pointed 

 head angles, will enable observers easily to recognize the species. 

 The head also is easily separable at the facial sutures, and this cha- 

 racter is worthy of notice. 



Locality. — Lower Ludlow Rock, Vinnal Hill, Ludlow. 



2. AciDASPis Caractaci, Salter. PI. VI. figs. 15-17. 



A. Caractaci, Salter, Mem. Geol. Surv. Decade 7. p. 7 of text 

 attached to plate 6. 



A. semiuncialis, capite semilunari convexo, glabella late triangulata tubercu- 

 lata, a genis convexis bene distincta, utrinque bilobata ; lobo basali centralem 

 aequante rotundo circumscripto, quani secundo duplo latiore, hoc distinc- 

 tissimo obovato ; superiore obsolete : [cervice — ?] thorace axi convexo, 

 pleuris ad apices deflexis bispinosis ; cauda 12- (vel 14- ?) dentata, spinis pri- 

 mariis fortibus paullura divaricatis, terminalibus minutis 6, externis 2 (vel 3), 

 axi convexo. 



The foregoing description of this species, but no figure, is given in 

 the Decade above referred to. 



Locality. — It is a common fossil in the fine yellow Caradoc (or 

 Bala) sandstone of Gretton, Shropshire ; a locality rich in trilobites 

 and shells. 



VOL. XIII. — PART I. Q 



