F. R. Cowper Reed — Some Wenloch Species of Lichas. 3 



vol. vi, pp. 235-239, pis. xxvii and xxvii his) has led me to make 

 the following notes upon them. I have also had the privilege, through 

 the kindness of Dr. Arthur Smith Woodward, F.R.S., of examining 

 the specimens in the British Museum (Nat. Hist.), Cromwell Road. 



'Lichas (Corydocephalus) anglious (Beyrich). (PI, I, Tigs. 1,'2.) 



Lichas Bueklandi, Fletcher {pars) : Q.J.G.S., 1850, vol. vi, p. 235, pi. xxvii, 

 figs. 2, 3, 4, ?5, 5« {non figs. 1, la) ; pi. xxvii bis, figs. 1, 1«, lb. 



There is considerable variation in the degree of development of 

 the spines on the pygidial margin of this species. A similar 

 variation is noticeable in Cheirurus bimiicronatus and the species 

 of Acidaspis from the same beds. The relative length of the axis 

 of the pygidium also shows marked individual differences. Fletcher 

 figured one specimen (op. cit., pi. xxvii, figs. 5, 5a) which he 

 described as a young individual, and probably it should be regarded 

 as such. But there are two well-marked and constant varieties 

 which show definite features separating them from the type-form, 

 and in fact are more abundant than the latter. 



(i) The first variety , which may be called wenlocJcensis (PL I, Fig. 1), 

 has a pygidium which is subquadrate in outline, and has almost 

 a straight posterior border. The nine marginal spines are unequally 

 developed ; the first two pairs are strong and of equal size, but the 

 third pair, situated at the lateral corners of the posterior margin, 

 are much stouter and larger, projecting nearly straight backwards 

 behind the pygidium. Between them lie three equidistant smaller 

 spines, the median one of which is generally the largest. Minute 

 prickles are in some specimens noticeable along the margin between 

 the spines, A shallow groove parallel to the posterior edge of the 

 pygidium and marking off a distinct border, but not crossing the 

 post-axial median piece, is present on the lateral lobes behind 

 the second pair of pleurae. A similar though fainter groove is 

 distinguishable on the pygidium of the type-specimen and type-form 

 figured by Fletcher (op. cit., pi. xxvii bis, figs. 1, la), and in the 

 other specimen regarded by him as a young individual (pi. xxvii, 

 figs. 5, 5a), but no mention of it is made in his description. 



The posterior half of each of the two pairs of pleurae behind the 

 pleural furrow in the variety wenlochensis is also remarkably narrow 

 in comparison with the anterior portion. In Fletcher's figure of 

 the type-form the posterior portion is made broader than it is in 

 reality in the specimen. 



From the above remarks it will be seen that the disting-uishina; 

 features of this variety are the general shape of the pygidium and 

 the development of the lateral spines. The thorax and head-shield 

 in complete specimens show no points of difference from the type- 

 form which can be established as constant. 



(ii) The second variety (PL I, Fig. 2), of which there are also 

 complete specimens in the Woodwardian Museum, likewise exhibits 

 its distinctive features only in the pygidium. In this form there are 

 only eight marginal spines, the posterior median one being absent or 

 merely represented by a small prickle. The shape of the pygidium 



