100 F. R. Cowper Reed — TrilobUes, Saver/ordwest. 



Dimensions. ^^ 



Length 29 



Length of head 10 



Length of thorax ... ... ... 14 



Width of thorax 20 



Affinities, — The glabella of this species appears to bear a con- 

 siderable resemblance to A. callipareos, Wyv. Thomson.^ Double 

 spines to the extremities of the pleurae are found in the Bala species 

 A. Caractaci, Salter," and the pygidium is somewhat similar to this 

 species, but the marginal spines are unequal in strength, and the 

 head-shield is completely different. A. evolnta, Tornquist,^ from 

 the Lept£ena Limestone, of which only the head-shield has been 

 described, possesses a somewhat similar lobation of the glabella 

 with a broad occipital ring and occipital lobes. A. Jamesi, Salter,* 

 and A. bispinosus, McCoy, ^ two well-characterised British Ordovician 

 forms, are quite distinct, save for the separation of the median lobe 

 of the glabella and the pair of short occipital spines. 



Note. — This new species appears also to be represented in the 

 Slade Beds, from which Mr. Turnbull has recently obtained some 

 specimens, 



AciDASPis (Ceratocephala) sladensis, sp. nov. 

 (PI, IV, Figs, 8-12.) 



Another and smaller species of Acidaspis occurs in the Slade 

 Beds ; only the head-shield and the pygidium are known, but the 

 specimens are nearly complete and in a good state of preservation. 



Description. — Head-shield semicircular, moderately convex. 

 Glabella oval, nearly as wide as long ; median lobe convex, 

 cylindrical, fairly well marked off from the lateral lobes, expanded 

 a little in front, gently rounded or subtruncate anteriorly. Anterior 

 pair of lateral lobes oval, convex, less than one-third the length of 

 glabella ; posterior pair oval, convex, nearly twice as large as 

 anterior pair, not strongly marked off from them. First pair of lateral 

 furrows short, curved back to meet second pair ; second pair weak 

 between lateral lobes, but continued backwards more strongly along 

 inner side of second lateral lobes to enter occipital furrow. Occipital 

 furrow strong, wide, horizontal ; occipital ring broad, nearly one- 

 third the length of glabella, provided with large median tubercle 

 and obscure traces of small occipital lobes ; margin furnished laterally 

 with pair of posteriorly directed divergent long spines. Axial 

 fun'ows distinct, arched outwards. Fixed cheeks swollen, curved, 

 widening posteriorly to nearly the width of glabella. Ocular ridge 

 narrow, raised, rounded. Eyes small, situated wide apart, and far 



1 Wyville Thomson: Q.J.G.S., vol. xiii (1857), p. 208, pi. vi, figs. 11, 12. 



2 Salter: ibid., p. 211, pi. vi, figs. 15-17, 



■^ Tornquist: Undersokn. Siljans, Trilobitf, (1884), p. 28, t. i, fig. 24. 

 * Salter: Mem, Geol. Surv., dec. vii (1853), pi. vi, figs. 1, 2, 3. 

 ^ Salter: ibid., p. 4, pi. vi, fig. 4, 



