4 TRILOBITES OF GIRVAN. 



pair horizontal, rather behind middle of axis, touching in centre a prominent 

 rounded tubercle. Limb convex, marked off from axis by strong continuous 

 furrow. Border wider than that round head-shield, and provided with a pair of 

 short lateral spines at about two-thirds of the distance from anterior end of 

 pygidium. 



Remarks. — The foregoing description is based on an examination of the type 

 specimens, and supplements earlier diagnoses, which are inadequate. This typical 

 Bala species, as defined by M'Coy and Salter, has only been recognised in the 

 Drummuck Group (Upper Bala) of the Girvan area. The examples of the genus 

 from the Llandeilo of Balclatchie, attributed to this species, belong to a distinct 

 form allied to A. maccoyi, which is described below. 



Collections. — Mrs. Gray ; Museum of Practical Geology, Jermyn Street. 



Horizon and Localities. — Drummuck Group (U. Bala) : Thraive Glen and Lady 

 Bum (Starfish Bed). 



2. Agnostus girvanensis, sp. nov. Plate I, figs. 2 — 4. 



1878. Agnostus trinodus, Etheridge, juu., Proc. Roy. Phys. Soc. Edinburgh, vol. iv, p. 173. 



1879. Agnostus agnostiformis, Nicholson and Etheridge, e.p., Mon. Silur. Foss. Girvan, fasc. ii, 

 p. 200, pi. xiv, fig. 6. 



1899. Agnostus agnostiformis, e. p., Mem. Geol. Surv., Silur. Rocks Brit., vol. i, Scotland, pp. 509, 

 514, 688. 



Specific Characters. — General shape oblong, rounded. 



Head-shield rounded, convex, forming about two thirds of a circle ; slightly con- 

 tracted at base. Glabella semi-cylindrical, gently convex, rounded at front end, 

 about one third the width and two thirds the length of the head-shield ; with two 

 small transverse triangular lobes at its base meeting in middle line, and separated 

 off from rest of glabella by strong oblique furrows. A transverse weak groove, 

 curved or slightly angulated forwards, crosses the glabella rather in front of the 

 middle, and immediately behind it is situated a small but distinct median tubercle. 

 Axial furrows strong, subparallel, but diverging at base outside the basal lobes of 

 glabella. Limb of uniform width, feebly convex, sloping down regularly on all 

 sides to margin, crossed by 2 — 3 fine, radiating impressed lines, of which two are 

 usually in front of the glabella. Small subtriangular area marked off on each side 

 at posterior lateral angle by strong curved furrow. Border of head-shield narrow, 

 rounded, ending in short spine at genal angle, and separated from limb by strong, 

 broad marginal groove. 



Thorax of two segments. Axis wide, with pair of strongly defined, oval, lateral 

 swellings. Pleura' very short, broad, grooved medianly, and notched so as to present 

 bilobate tips. 



Pygidium semi-elliptical or oval, rounded, convex, slightly constricted in front. 



