132 TRILOBITES OF GIRVAN. 



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

 Horizon a n cl Locality. — Balclatcbie Group (Llandeilo) : Dow Hil 



Genus DINDYMENE, Corda. 

 1. Dindymene cordai, Etlieridge and Nicholson, 1878. Plate XVII, figs. 9 — 11. 



1878. Dindymene cordai, Nicholson and Etlieridge, Men. Silur. Foss. Girvan, fasc. i, p. 115, 

 pi. viii, fig. 8, and p. 116, figs. 5 a, b. 

 ? 1880. Siaurocephahis ? sp. ind., Nicholson and Etlieridge, op. cit., fasc. iii, p. 283, pi. xix, fig. 3. 

 1899. Dindymene cordai, Mem. Geol. Surv., Silur. Bocks Brit,, vol. i, Scotland, pp. 517, 524, 672, 

 689. 



Specific Characters. — Head-shield almost semicircular, slightly parabolic, 

 strongly convex from side to side and from back to front; the sides are 

 suddenly bent down on each side of the glabella, giving an angulated appear- 

 ance to the front aspect. Glabella strongly convex, higher than cheeks, most 

 elevated at about one third its length from base ; pyriform in shape, and pro- 

 jecting in front of the cheeks ; widest at anterior end, narrowing posteriorly to 

 base to about half the anterior width. No lateral furrows or lobes. Axial 

 furrows deep, strong, nearly straight, converging posteriorly at about 30°. Occipital 

 furrow strong. Occipital ring narrow. Cheeks strongly bent down on each side, 

 tumid, not so elevated as glabella, subtriangular in shape, arched outward in front 

 of genal angles, more than twice as wide as glabella at base. Genal angles broadly 

 rounded. Neck segment rounded, narrow, marked off by strong furrows, and 

 passing at genal angles into raised, rounded, smooth, lateral border surrounding 

 head-shield and marked off from cheeks and glabella by strong, continuous, 

 marginal furrow. No facial sutures or eyes. Surface of glabella and cheeks 

 uniformly tuberculated, and cheeks in addition pitted. A single large median 

 tubercle situated at about one third the length of the glabella. 



Thorax as long as head-shield, consisting of ten segments. Axis convex, 

 prominent, gradually tapering; axial rings rounded, with small median tubercle 

 on each between a pair of lateral tubercles; on fourth ring a strong median 

 spine (base only preserved) takes the place of the median tubercle. Pleura? 

 rounded, divided into a posterior, prominent, raised, rounded ridge and a much 

 narrower, lower, rounded, anterior band; pleuras in contact only for a distance 

 about equal to width of axis, then free and separate, tapering to long free points. 

 Pleurae strongly arched downwards, and successively more curved backwards 

 towards pygidium till they lie almost parallel with axis. A single row of minute 

 tubercles ornaments each pleura. 



