874 DR F. R. C. REED ON THE 



.acquainted with any interiors. The brachial valves from Craighead referred by him 

 to L. llandeiloensis (op. cit., pi. xii, figs. 27-29) precisely agree in shape and orna- 

 mentation with the Craighead types of L. Grayse, and the ridging of the pedicle- 

 valve in the latter is explained by the presence of the internal median ridge and 

 spine in the brachial valve as there pictured. The true L. \Plect.\ llandeiloensis 

 has for its type the Ardmillan shell (Davidson, op. cit., pi. xii, fig. 26 only), and is 

 completely distinct (see p. 876) ; and it does not occur in the Stinchar Limestone 

 Group. There is no internal concentric ridge in the pedicle-valve of L. Grayge as 

 there is in L. llandeiloensis, and the external ornamentation, of which Davidson 

 gave an incorrect description, is quite different. 



We must refer L. Grayse to the genus Leptella, Hall and Clarke, to which Hall 

 and Clarke, # owing to Davidson's confusion of the Craighead and Ardmillan forms, 

 were led to refer L. llandeiloensis. 



Leptella % pseudoretrojlexa, sp. nov. 

 (Plate XIII, figs. 18-26.) 



1 1870. Strophomena retroflexa, Salter, Davidson (pars), Mon. Brit. Foss. Brack., vol. iii, pt. vii, p. 298, 

 pi. xlii, rig. 17 (non figs. 15, 16). 

 1883. Strophomena retroflexa, Salter, Davidson (pars), ibid., vol. v, Silur. Suppl., pp. 195, 227 

 (non pi. xv, figs. 7, 8). 



Shell transversely semicircular to semielliptical, subalate, with pointed cardinal 

 angles, widest along hinge-line, compressed, flattened, weakly piano- to concavo- 

 convex ; cardinal angles acute, usually pointed at about 60°, and often slightly 

 produced ; hinge-line straight, minutely crenulated along whole length (?). Pedicle- 

 valve flat or slightly concave, very shallow ; beak small, slightly elevated, pointed, 

 not incurved ; hinge-area triangular, inclined to plane of valve at 45°-60°, with 

 narrow convex triangular deltidium covering delthyrium. Brachial valve gently 

 convex, deeper than other valve, with very weak median depression occasionally 

 present ; beak small, inconspicuous ; hinge-area triangular, rather narrower than that 

 of opposite valve, inclined nearly at right angles to plane of valve, with small 

 convex triangular deltidium covering fissure. Surface of valves covered with 

 numerous small straight radiating ribs of equal size regularly arranged, closely 

 placed, increasing rarely by intercalation at about half their length, so as to number 

 60-90 on margin ; interspaces rather wider than ribs, coarsely pitted ; fine con- 

 centric striation present. Interior of pedicle-valve with pair of small stout teeth 

 and numerous coarse irregularly spaced and broken rugae radiating outwards and 

 becoming more prominent and thicker towards margin of valve, where they unite 

 with a thick interrupted submarginal concentric ridge outside which the extern;! 1 

 ribbing shows ; muscular scar broad, indistinctly defined in front, transverse 

 in shape, about one-third the length of shell, composed of pair of flabelliform 

 * Hall and Clarke, op. cit., Brach., i, p. 293, pi. xva, figs. 12-16. 



