140 TRILOB] TES OF GIRVAN. 



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

 Geology; Woodwardian [Sedgwick] Museum. 



Horizons and Localities. — Drummuck Group (U. Bala) : Drummuck ; Tliraive 

 Glen. Saugh Hill Group (M. Llandovery) : Newlands ; Woodland Point. 

 Camregan Group (U. Llandovery) : Penwhapple Glen ; Bargany Pond Burn. 



1. Cheirurus gelasinosus (Portlock), 1843. Plate XVIII, figs. 5, 0. 



1843. Amphion gelasinosus, Portlock, Geol. Bep. Londond., p. 289, pi. iii, fig. 4. 



— Arges planospinosus, Portlock, ibid., p. 272, pi. v, fig. 9. 



1S45. Cheirurus gelasinosus, Beyrich, TJeber biihrn. Trilob., pt, i, p. 19. 



1851. Cheirurus gelasinosus, Salter, Quart. Jouru. Geo!. Soc, vol. vii, p. 170, pi. viii, fig. 1. 



1853. Cheirurus gelasinosus, Salter, Mem. Geol. Surv., dec. vii, art. 2, p. 11. 



1859. Cheirurus gelasinosus, Murcliisou, Siluria, 2nd ed., p. 538. 



1864. Cheirurus gelasinosus, Salter, Mori. Brit. Trilob.. p. 71, pi. v, figs. 6 — 8. 



1876. Cheirurus gelasinosus, Armstrong and Young, Cat. West. Scot. Foss., p. 15. 



1877. Cheirurus gelasinosus, Woodward, Cat. Brit. Foss. Crust., p. 30. 



1879. Cheirurus gelasinosus, Nicholson and Etheridge {e. p.), Mon. Silur. Foss. Girvan, fuse, i, p. 100 



(non pi. vii, figs. 5, 6). 

 1899. Cheirurus gelasinosus, Reed, Quart. Jouru. Geol. Soc, vol. lv, p. 748. 



Remarks. — Though the head-shields attributed to this species by Nicholson and 

 Etheridge (op. cit.) belong to the subgenus NieszkowsJcla (p. 142) and are quite 

 distinct from the true G. gelasinosus, yet the latter species really occurs in the 

 limestone of Craighead, and also of Minim tion. Salter in 1851 (loc. cit.) gave a 

 good figure of a head-shield of this species from Craighead. The Russian species 

 G. exsul, C. spinulosus, and C. gladiator, which come from approximately the same 

 stratigraphical horizon, have very similar head-shields, and are closely allied forms. 



There is a portion of the thorax of a large Cheirurus from Craighead which 

 belongs presumably to this species, as it is of the right size and proportions to 

 fit the head-shield. But the thorax of C. gelasinosus has not been previously 

 described. This specimen shows a convex cylindrical axis about two thirds the 

 width of the pleurae, which consist of an inner straight portion traversed by a short 

 oblique furrow, and of an outer, rounded, and unfurrowed, gently curved portion, 

 tapering to a free point. The base of this outer portion is somewhat swollen, and 

 at its junction with the inner portion the pleura is constricted, and it is here that 

 the fulcrum is situated. The tubercle situated at this point in C. bimucronatus is 

 not apparent, perhaps owing to the state of preservation, but in other respects 

 the thoracic rings appear to be almost indistinguishable from those of this species. 



Some fragments of head-shields from the Baiclatchie conglomerate, wh ich are 

 in Mrs. Gray's collection, may belong to this species. 



Collections. — Mrs. Gray ; Museum of Practical Geology. 



