ACIDASPIS DALECARLICA. 119 



furnished with a narrow rounded border. The surface of the fixed cheeks is 

 reticulated as well as tuberculated. 



The thorax of this species as figured and described by Wyville Thomson (op. cit., 

 pi. vi, figs. 4 a, 5) agrees closely with that belonging to the type of A. <jrai/x, for the 

 type of this species luckily consists of an entire individual. But the pleural spines 

 are not denticulate, and the supplementary marginal spines seem to be absent. 

 The pygidium also bears a very close resemblance to this species, except in the 

 number of the marginal spines and their want of denticulations. Specimens showing 

 the above characters are in Mrs. Gray's collection. As already stated, I have some 

 doubt whether the species A. lalage and A. >jra;/se are truly distinct. At any rate 

 the thorax, with an imperfect head-shield attached, which Nicholson and Etheridge 

 figured as belonging to A. lalage (op. cit., pi. viii, fig. 17) is completely different to 

 that figured by Wyville Thomson ; the pleural groove is much narrower and further 

 forward, the ridge bounding it behind is much stronger than the anterior marginal 

 one ; the long lateral spine is in direct continuation of the main ridge, and the 

 anterior ridge is furnished with a short straight spine projecting horizontally. 

 Both ridges are also ornamented with a row of 7 — 9 tubercles. It should probably 

 be referred to A.hystrix (n.v.) The true thorax and pygidium of A. lalage may still 

 remain to be discovered, unless A. grai/ae proves to be identical. 



Collections. — Mrs. Gray (f. M.) ; Edinburgh Museum. 



Horizon and Localities. — Balclatchie Group (Llandeilo) : Balclatchie ; Dow- 

 Hill. 



S. Acidaspis dalecarlica, Tornquist, 1884. ? Plate XVI, fig. 7. 



1884. Acidaspis dalecarlica, Tornquist, Siljansom. Trilobitf. (Sver. Geol. Undersokn., Eer. C, No. 66) 

 p. 27, pi. i, fig. 23. 



A small pygidium, about 5 mm. wide, from Shalloch Mill is probably identical 

 with Tornquist's species A. dalecarlica (op. cit.) from the Trinucleus Shales of 

 Sweden. It is distinct from any British form hitherto described. 



Description. — Pygidium flattened, transverse, nearly twice as broad as long 

 (including spines), with strong rounded ridge on front margin. Axis short, wide, 

 of two rings. Lateral lobes small, depressed, traversed by one strong pair of ridges 

 which are continued into the third pair of spines ; border raised and furnished with 

 six pairs of spines, of which the first two pairs are equidistant, straight, subequal, 

 projecting backwards and slightly outwards; the third pair is larger, stouter, and 

 longer than any of the others, and is produced backwards to about twice the length 

 of the second pair ; the fourth pair is small and [tartly overlapped by the third pair. 



