LICHAS (PLATYLICHAS) GRAYI. 99 



Specific Characters. — Pygidium transversely subquadrate, nearly twice as 

 broad as long. Axis short, broad, convex, rather more than half the length of the 

 pygidium, and occupying the middle third of its width, scarcely tapering at all 

 posteriorly, abruptly truncated, and connected with posterior margin by narrow, 

 low, straight, post-axial ridge (as in typical members of the section Corydo- 

 cephalus). Two axial rings appear to be present at the front end of the axis, but 

 this part is not well preserved. Lateral lobes bent down, consisting of three pairs 

 of pleura?. First two pairs of pleurae subequal, lanceolate, strongly bent back 

 beyond the approximate fulcrum, and produced into free points beyond margin. 

 The points of the second pair extend beyond the posterior end of the pygidium. 

 Each of the two first pairs of pleurae is marked with a submedian pleural furrow. 

 Third pair of pleurae very short and broad, without pleural furrows ; separated in 

 middle by post-axial ridge and deep narrow notch in pygidial margin. Each 

 pleura of the third pair ends on the margin with two points. Ornamentation not 

 preserved. 



Remarks. — This peculiar little pygidium, of which I have only seen the one 

 example here figured, agrees with L. wesenbe?yjensis, Schmidt, 1 in its general 

 characters, and especially in the double-pointed third pleurae. It differs in its 

 more transverse shape, the stronger backward curvature of the two first pairs of 

 pleurae, and in the prolongation of the second pair behind the posterior margin. 

 From L. geihiei it differs in the shape of the axis, the greater width of the 

 pygidium, and the prolongation of the second pair of pleurae ; and it comes from 

 a different stratigraphical horizon. A supposed variety of L. loesenbergensis has 

 been described by Clarke 2 as var. paulianus from the Trenton Limestone of 

 Minnesota, but the small pygidium figured by him differs more than ours does 

 from the typical Russian examples of the species. 



Collection. — Woodwardian [Sedgwick] Museum. 



Horizon and Locality. — Balclatchie Group (Llandeilo) : Dow Hill. 



5. Lichas (Platylichas) grayi, Fletcher, 1850. 



1848. Lichas, sp. hid., Salter, Mem. Geol. Surv., vol. ii, pt. i, p. 340, pi. viii, fig. 8. 



1850. Lichas grayii, Fletcher, Quart. Journ. Geol. Soc, vol. vi, p. 237, pi. xxvii, fig. 8 ; pi. xxvii 



bis, figs. 3, 3a, 3b. 

 1854. Lichas grayii, Morris, Cat. Brit. Foss., 2nd ed., p. 110. 



1 Schmidt, ' Rev. Ostbalt. Silur. Trilob.,' pt. ii, pi. vi, fig. 2. 



'-'Clarke, 'Lower Silur. Trilob. Minnesota, p. 744, figs. 62—64 (Final Eep. Geol. Nat. Hist. Sur 

 Minnes., vol. iii, 1894). 



