ORDOVTCIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 849 



primaries, except one or two shorter intercalated ones on the outer slopes of the. lobes. 

 This shell much resembles the " Caradoc" form of the species figured by Davidson* 

 from Cefn Rhyddan, and is distinguishable from the Wenlock type, though it is 

 perhaps hardly worthy of a varietal name. 



Horizon. — Whitehouse Group. 



Localities. — Whitehouse Bay, Shalloch Mill. 



Subgenus dalmanella, Hall and Clarke. 

 Orthis {Dalmanella) basalis, Dalman. 

 (Plate IX, fig. 7.) 

 1827. Orthis basalis, Dalman, Svensk. Vet. Ahad. Haudl., p. 116, pi. ii, fig. 5. 

 1868. Orthis basalis, Dalman?, Davidson, Mon. Brit. Foss. Brach., vol. iii, pt. vii, p. 217, pi. xxvii, 



figs. 10, 11. 

 1883. Orthis el eg antida, Dalman, Davidson (pars), op. cit., vol. v, Silur. Suppl., pp. 178, 226. 



There are many specimens from the Llandovery of Woodland Point which have 

 been assigned to the species 0. elegantula, but should be placed in 0. basalis, Dalman, 

 for they completely agree with the Falfield shells which Davidson t correctly referred 

 to this species, and with specimens from Gotland named by Lindstrom. They differ 

 especially from 0. elegantula by the lower beak, lower hinge-area, and less inflation of 

 the pedicle-valve. The shape of the shell, moreover, is circular or nearly so, instead 

 of oval. The pedicle-valve is often subcarinate, and especially swollen in the middle, 

 while the opposite valve is only very weakly convex, most so near the inconspicuous 

 beak, or may be flattened or slightly concave, with a trace of a weak median depression 

 close to the beak. The ribbing is not very regular ; the primaries are fairly equal 

 in strength, but the ribs increase in number either by the intercalation of 2-4 rather 

 finer ones or less often by their unequal and rather irregular bifurcation or even 

 trifurcation once or twice at one-third to one-half their length. Every fourth or fifth 

 rib is rather stronger, and this greater strength is maintained even to the margin. 

 The larger shells are about 9-10 mm. in diameter, and a trifle less in length. I have 

 not seen any well-preserved interiors from Woodland Point. 



Horizon. — Saugh Hill Group. 



Locality. — Woodland Point. 



Orthis (Dalmanella) crassa, Lindstrom ? 

 (Plate IX, figs. 8-10.) 

 1860. Orthis crassa, Lindstrom, Gotlands Brachiopoder, p. 369. 



1883. Orthis elegantula, Dalman, Davidson (pars), Mon. Brit. Foss. Brach., vol. v, Silur. Suppl., 

 pp. 178, 226. 



This species J appears to be represented at Penkill by some specimens labelled 

 0. elegantula by Davidson. Examples of O. crassa from Gotland, named by 

 Lindstrom, which I have examined, agree very closely with this Girvan shell in 



* Davidson, Mon. Brit. Foss. Brach., vol. iii, pt. vii, pi. xxvi, fig. 12. 



t Davidson, op. cit., iii, p. 217, pi. xxvii, figs. 10, 11. { Davidson, op. cit., xxiii p. 213, pi. xxvii, figs. 17-19. 



