F. JR. Cowjjer Reed — Trilohites, Haverfordwest. 101 



back, nearly opposite middle of posterior lateral lobes. Neck 

 segment rounded, narrow, widening laterally, marked off from 

 fixed cheeks by strong furrow. Facial sutures cut posterior margin 

 of bead-shield far out. Anterior margin of head-shield provided 

 with narrow raised rounded border with strong marginal furrow. 

 Surface of head-shield coarsely tuberculated. Thorax unknown. 



Pygidiutn broadly semicircular, transversely expanded, almost 

 flat ; posterior margin furnished with seven pairs of equidistant short 

 radiating spines of equal length and size. Axis convex, short, bluntly 

 terminating inside narrow raised rim, not quite one-third the width 

 of the pygidium, composed of two segments and of a small articulating 

 ring in front ; first segment formed by a complete rounded ring ; 

 second segment broader and bearing a median pair of large tubercles 

 and a lateral pair of smaller ones. Lateral lobes flat, horizontally 

 extended without definite pleural ridges, but with 2-3 large elongated 

 tubercles. Marginal rim raised, rounded, narrow, with regular double 

 row of tubercles. Marginal spines granulated. (PI. IV, Figs. 11, 12.) 



DlBIENSIONS. jjjjj^^ 



Length of head-shield ... 3'0 



Length of pygidium (without spines) 1'5 



Width of ditto 4-0 



Affinities. — This species has many of the characters of A. Lalage, 

 Wyv. Thomson,^ particularly in the lobation of the glabella and 

 occipital spines, but it differs in the coarse tuberculation of the 

 head-shield and in the features of the pygidium. The pygidium, 

 indeed, more resembles that of A. hystrix, Wyv. Thomson,^ but the 

 latter has distinct pleural ridges on the lateral lobes, and no pair 

 of conspicuous tubercles on the second axial segment. A. Grayce, 

 Etheridge,^ is too imperfectly known, but the pygidium is certainly 

 distinct. 



Both these species, A. sladensis and A. Tiirnhidli, belong to the 

 subgenus Geratocephala, Warder, 1838 (type C. goniata, Warder), 

 as understood and limited by Clarke.* Van Ingen * suggests using 

 the divisional names Odontopleura, Selenopeltis, Ceratocephala, Dicra- 

 nurus, Acidaspis, and Ancyropyge in a generic sense, but this does 

 not seem desirable, as the value of these groups is scarcely of so 

 high a rank. 



Family LICHADID^. 



LiCHAs (Metopolichas) affinis, Angelin, var. 



(PI. IV, Fig. 13.) 



There is one fairly well-preserved pygidium of a species of Lichas 

 from the Slade Beds which cannot be referred to any common British 



1 Nicholson & Etheridge : Men. Foss. Gii-van, fasc. i (1878), p. 121, pi. viii, 

 iigs. 20-22 {non figs. 17-19). 



2 Ibid., p. 123, pi. Tiii, fig. 25. 



3 Ibid., p. 126, pi. viii, fig. 26 ; pi. ix, figs. 1-7. 



* Clarke : Tenth Eeport New York State Geol. (1891), p. 67, pi. i, fig- 1- 



^ Yan Ingen: School of Mines Quarterly, vol. xxiii (Nov. 1901), No. 1, pp. 36-39. 



