BRITISH SILURIAN BRACHIOPODA. 203 



convex. Surface of both valves covered with fine, longitudinal, radiating, thread- 

 like radii, with shorter and narrower ones occasionally intervening between each of 

 the larger pair, and especially so in the proximity of the front and lateral margins. 

 From five to eight of these ridges occupy the breadth of a line. The interspaces between 

 the longitudinal radii are about three times the width of each ridge. The surface of the 

 valves are also covered with horizontal or concentric, narrow, rounded ridges with inter- 

 spaces of about equal breadth, as may be seen in the enlarged drawing, fig. 1 c, of our 

 Plate. The perpendicular and horizontal series of radii or ridges, produce on the 

 surface of the valves a beatifully reticulated sculpture, to which the rows of bead-like 

 projections at the points of intersection give additional prominence. 



The size of Mrs. R. Gray's specimen, when complete, cannot have measured less 

 than 1 inch and 9 lines in length by 1 inch and 3 lines in breadth. The bead-like 

 projections recall those of Lingula tenuigranulata^ M'Coy, a closely allied species, and 

 which differs from the one under description by its much more finely and closely reti- 

 culate sculpture. 



132. Lingula quadrata, Eichwald. Dav., Sil. Sup., PI. XVII, figs. 2, 3. 



Lingula quadrata, Eichwald. Zool. Specialis, vol. i, p. 273, pi. iv, fig. 2, 1829. 



— — De Verneuil. Geol. of Russia, vol. ii, pi. i, fig. 10, 1845. 



— — d' Eichwald. Letlisea Rossica, periode ancienne, vol. i, p. 917, 



1859. 



— — Dav. Geol. Mag., new series, vol. iv, p. 16, pi. ii, figs. 2, 3, 



1877. 



Shell longitudinally oval, tapering obtusely at the beaks, rounded in front, sides 

 subparallel ; valves moderately convex, surface marked with concentric lines of growth, 

 and slightly indented longitudinal striae along the middle of the shell. 



Length 1^ inches ; breadth 1 inch I line. 



06s. — After comparing several Scottish specimens of this fine Lingula with Russian 

 examples from Reval, given to me by Prof. F. Schmidt, I arrived at the conclusion that 

 the specimens found by Mrs. R. Gray in the Llandeilo Limestone at Craighead Quarry, 

 near Girvan, in Ayrshire, were referable to the Russian type of Lingula quadrata. 

 In Russia the shell attains to dimensions equal to if not exceeding those of the shell 

 we have described as L. Canadensis, but our Scottish examples do not quite attain those 

 proportions. 



