ORDOVICTAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 905 



triangular delthyrium in each valve. In this specimen there are about 50-60 ribs on 

 each valve, all of equal strength on the margin and equidistant, except near the 

 cardinal angles, where they are more crowded ; the ribs are rounded, straight, simple, 

 and separated by rather wider interspaces ; about half the number of ribs are primary, 

 the others arising by intercalation usually close to the beak ; all are concentrically 

 lineated. In some of the other specimens from Shalloch Mill, perhaps attributable 

 to this species, there are 3-4 considerably finer radial lines between the larger 

 ribs, as are shown in the shell from Corwen. The interior is very inadequately 

 known, but Davidson's figure of the interior of a supposed ventral valve (op. cit., 

 pi. xi. fig. 2 1) looks more like the interior of a brachial valve. One imperfect interior 

 of a pedicle-valve from Shalloch Mill in Mrs Gray's collection shows traces of weakly 

 impressed short fiabelliform diductors. 



Dimensions (Davidson's type, pi. xvi. fig. 8). — Length, 21 mm. ; width, 35 mm. 



Horizon. — Whitehouse Group. 



Locality. — Shalloch Mill. 



Strophomena valens, sp. nov. 

 (Plate XIX, figs. 13-17.) 



Shell semicircular to transversely semielliptical, nearly twice as wide as long, 

 compressed, slightly resupinate, concavo-convex ; maximum width of shell along 

 hinge-line ; cardinal angles rectangular or bluntly pointed at about 75°. Pedicle- 

 valve gently concave, with rather prominent retrorse pointed beak rising a little above 

 hinge-line ; hinge-area triangular, steeply inclined to plane of valve, with rather 

 narrow delthyrium. Interior with strong short dental plates diverging at right 

 angles, and large transversely subcircular muscle-scar about one-third the length of 

 the valve, composed of a pair of radially ridged flabellate diductors not deeply sunk 

 nor sharply defined in front. Brachial valve gently convex, with small inconspicuous 

 beak ; hinge-area narrower than in opposite valve. Interior of brachial valve with 

 strong broadly oval bilobed cardinal process, the inner faces of the lobes elongated, 

 sublanciform, parallel, closely placed, lying in plane of valve, with posterior face 

 grooved ; crural plates thick, short, slightly curved, diverging at more than right 

 angles ; muscle-scars faint, weakly impressed, separated by low broad median ridge. 

 Surface of shell covered with very fine numerous straight radiating closely placed 

 radii, increasing by intercalation, numbering about 350-400 on margin, with every 

 6th, 7tli, or 8th one rather larger, all crossed by fine concentric striee. (The ribs 

 show strongly round the margins in internal casts.) 



Dimensions. — Length, 22 mm. ; width, 36 mm. 



Horizon. — Drummuck Group (Starfish Bed). 



Locality. — Thraive Glen. 



Remarks,— This species is only found in the Starfish Bed, but some of the 



