ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 893 



valve in Mrs Gray's collection which plainly shows them was labelled by Davidson 

 " Orthis Actonix, young." In outline and convexity the shell recalls Str. Orbignyi, 

 Dav., # of the Wenlock Limestone, but in ornament it is more like some of the Welsh 

 specimens referred wrongly by Davidson to Str. shallochensis.i It is possible that 

 it is related to Str. retrojlexa, Salter,} and the muscle-scar in the pedicle-valve and 

 convexity resemble Str. ungula, M'Coy.§ 



Stroplieodonta Jamesoni, sp. nov. 

 (Plate XVI, figs. 28-30 ; Plate XVII, figs. 1,2.) 



1883. Strophomena corrugate/la, Davidson (pars), Mon. Brit. Foss. Brarh., vol. v, Silur. SuppL, p. 192, 

 pi. xv, fig. 25 only (non tigs. 23, 24, 26). 



Shell semioval to subquadrate, widest along hinge-line, much compressed, 

 flattened ; cardinal angles subacute, rather less than right angles, usually slightly 

 produced, pointed, and subauHculate. Pedicle-valve much flattened, slightly raised, 

 and subcarinate along middle line ; margin occasionally slightly arched down ; beak 

 small, pointed, scarcely rising above hinge-line ; hinge-area narrow, linear, longitudin- 

 ally striated, steeply inclined, or nearly at right angles to plane of valve ; hinge-line 

 minutely denticulate ; delthyrium small, triangular, with convex deltidium. 

 Interior of pedicle-valve with very short small dental lamellae, large faint flabelli- 

 form diductors, and coarse pustules over surface in irregular radial lines. Brachial 

 valve gently concave on disc, flattened elsewhere ; beak small, inconspicuous ; 

 hinge-area narrower than in opposite valve. Interior imperfectly known. 



Surface of valves ornamented with 20-30 primary thread-like riblets, sometimes 

 slightly nodulose, equidistant, and of equal strength, curving back gently on each 

 side of middle line ; interspaces filled with 2-7 finer thread-like radii, of which one 

 or more, rather irregularly at one-third to three-fourths their length, increases to 

 size of primaries (or nearly so), so that marginally there are 100 or more subequi- 

 distant equal or subequal riblets with finer intermediate radii ; 4-6 strong widely 

 spaced short concentric rugse on each side close to hinge-line, bending out sharply 

 so as to meet it at very acute angles, not continued over disc. Interspaces generally 

 marked with short straight unbent transverse equidistant shallow pits, developed 

 somewhat irregularly over half or two-thirds the length of shell. 



Dimensions. — Length, 28 mm. ; width along hinge-line, 39 mm. 



Horizon. — Saugh Hill Group. 



Localities. — Woodland Point, Newlands. 



Remarks. — This shell is undoubtedly much like Str. corrugatella, to which 



species it was assigned by Davidson. But it differs in the greater flatness of the 



valves, the less transverse shape, the marginal corrugations on the valves near 



the hinge-line, the outward curvature of the riblets, and the different shape and 



* Davidson, op. cit., vol. iii, p. 306, pi. xlii, figs. 12-14. t Ibid., SuppL, vol. v, pi. xii, fig. 30. 



I Ibid., vol. iii, p. 298, pi. xlii, figs. 14-16 (?non 17). § Ibid., vol. iii, p. 296, pi. xlii, figs. 6-8. 



