142 TRILOBITES OF GIRVAN. 



1866. Cheirurus octolobatus, Salter, Mem. Geol. Surv., vol. iii, p. 323, pi. xviii, fig. 3. 

 1873. Cheirurus octolobatus, Salter, Cat. Camb. Silur. Foss. Woodw. Mus., p. 51. 



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



1877. Cheirurus {Actinopeltis) octolobatus, Woodward, Cat. Brit. Foss. Crust., p. 31. 



1878. Cheirurus clavifrons (?), Nicholson and Etheridge, Mon. Silur. Foss. Girvan, fasc. i, p. 101, 

 pi. vii, figs. 7, 8, ? 9 ; and fasc, ii, p. 202, pi. xiv, fig. 10. 



1891. Cheirurus (Actinopeltis) octolobatus, Woods, Cat. Type Foss. Woodw. Mus., p. 142. 



Remarks. — There exists much doubt whether C. octolobatus, M'Coy, is identical 

 with C. clavifrons, Dalra. ; and as we are not in a position at present to settle the 

 matter it seems safer to keep the British forms apart rather than to assume a 

 possibly non-existent specific identity. Moreover, so far as the Girvan specimens 

 indicate, the eyes are too far back for G. clavifrons as interpreted by Schmidt, 1 

 Brogger, 3 and other continental palaeontologists, and the posterior branch of the 

 facial suture diverges at a level between the second and third lateral furrows of 

 the glabella. The anterior part of the head-shield also differs in the amount 

 of bending down. 



The pygidia of 0. clavifrons and of the allied G. affinis, Angelin, are of a type 

 quite distinct from that associated with these Girvan head-shields. On the other 

 hand, these Girvan specimens agree minutely in the features of the head-shield, 

 thorax, and pygidium with those figured as G. octolobatus by Salter (op. cit., 1864), 

 though some of them are of a larger size, one head-shield measuring 27 mm. in 

 length. It may be remembered that Salter's type of this species (op. cit., pi. v, fig. 13) 

 came from Penwhapple in the Girvan area. There is in Mrs. Gray's collection one 

 excellent specimen of the whole thorax with pygidium attached, showing with great 

 clearness all the characteristic features of the species as described by Salter, except 

 that the axis is rather narrower. The species is rather common in the Sholeshook 

 Limestone of the Haverfordwest district. 



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



Horizon and Localities. — Drunmmck Group (IT. Bala): Drummuck; Thraive 

 Glen ; Penwhapple. 



4. Cheirurus (Nieszkowskia) unicus (Wyville Thomson), 1857. Plate XVIII, 



figs. 12—16. 



1857. Acidaspis unica, Wyville Thomson, Quart, Journ. Geol. Soc, vol. xiii, p. 209, \l. vi, figs. 



13, 14. 

 1857. Staurocephalus ? maclareni, Wyville Thomson, MS. (e. }>■), Coll. Mus. Prait. Geol. 

 1865. Staurocephalus ? U7iicus, Salter (e. p.), Mon. Brit. Trilob., p. 86, pi. vii, figs. 23, 24 (non 



fig. 22). 



1 Schmidt, ' Eev. Ostbalt. Silur. Trilob.,' pt. i, p. 153, pi. viii, figs. 4—6; pi. xvi, figs. 7—12. 



2 Brogger, * Die Silur. Et. 2 und 3,' p. 131, pi. v, figs. 1, 2, ? 3. 



