128 TRILOBITES OF GIRVAN. 



ridge is well developed, the anterior one being very narrow and not extending to 

 the base of the pleura. The half-pleura is a very narrow straight tuberculated 

 ridge lying closely pressed against the axis. The ends of the pleurse are gathered 

 closely together behind the axis, and then spread out in a fan-shaped manner to 

 form the tip of the tail. The narrow wedge-shaped post-axial piece separates the 

 pleura? of the opposite sides behind the axis. But, unfortunately, no example has 

 the extremity of the pygidium in a first-rate state of preservation. 



Linnarsson's figure of C. loveni does not indicate the pygidial characters very 

 minutely, but so far as can be judged they are not quite identical with those of the 

 Girvan specimens. Hence these latter may be recognised as a local variety and 

 termed var. girvanensis. 



G. loveni was recorded by Marr 1 in the Settle district in 1887, for the first time 

 in the British Isles. 



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



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

 Drummuck. 



3. Cybele cf. aspera, Linnarsson, 1869. Plate XVI, figs. 12, 13. 



? 1878. Cybele verrucosa, Nicholson and Etheridge, Mon. Silur. Foss. G-irvan, fasc. i, p. Ill (non 



fig. 5 c). 

 ? 1899. Cybele verrucosa, Mem. G-eol. Surv., Silur. Eocks Brit., vol. i, Scotland, pp. 509, 514, 688. 



Remarks. — A species of Cybele has been recorded from several horizons and 

 localities in the Girvan district as C. verrucosa, Dalman, but few of the specimens 

 in Mrs. Gray's or other collections which I have examined appear to correspond 

 precisely with this type. One from Craighead which, perhaps, may be referred to 

 it, is mentioned below, but the majority show features which do not agree with 

 C. verrucosa, as Loven- figured and described it, though later authors have widely 

 diverged from his definition, so that current synonymies have not much value. 

 Of other species of Cybele, G. aspera, Linnarsson, 3 appears to bear a greater 

 resemblance to the form from the Balclatchie Beds which is here described ; the 

 points of similarity are mentioned below. Unluckily, none of the specimens are 

 well preserved. In the head-shield from Ardmillan the glabella is strongly convex 

 and subclavate in shape, but the frontal lobe is not so transversely expanded as 

 is usual in G. verrucosa ; there are three pairs of deep lateral pits which are not 

 continued into the axial furrows, and thus mark off incompletely three pairs of 

 lobes, as in C. aspera, whereas in C. verrucosa there are true furrows; the anterior 



1 Marr, 'G-eol. Mag.' [3], vol. iv (1887), p. 35. 



2 Lovt'n, 'Ofv. K. Svensk. Vet, Akad. Forhandl.,' no. 3 (1845), p. 52, pi. i, fig. 5a. 

 :5 Linnarsson, ' Vestergotl. Camb. Silur. Aflagr.' (1869), p. 62, pi. i, figs. 11—13. 



