ORDOVICTAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 881 



sentatives of PI. scissa the transverse impression formed by the diductors can scarcely 

 be described as " saucer-shaped," for it is transversely oblong, broadly emarginate in 

 front, and consists of a pair of short broad strongly divergent subquadrate scars, 

 obscurely notched at their outer ends and in contact in the middle, with a small 

 adductor scar between them ; and from the outer angles of the diductors there is on 

 each side a pair of short divergent ridges or vascular trunks. The hinge-line is 

 crenulated as in PL llandeiloensis. 



Horizons. — (l) Camregan Group ; (2) Mulloch Hill Group ; (3) Saugh Hill Group. 



Localities. — (l) Bargany Pond Burn ; (2) Mulloch Hill ; (3) Newlands. 



Plectambonites segmentum (Angelin). 



1838. Leptama, segmentum, Angelin MS., Mus. Palseont. Suec. 



It is doubtful if the true PI. segmentum of Angelin (MS.) occurs in the Girvan 

 area, but there is one fairly well-marked variety represented at Woodland Point. 



The shells which Davidson # attributed to PI. segmentum from the Wenlock Shale 

 of Dudley, Build was, etc., are distinct from our variety, but are probably identical 

 with the Gotland form. 



Plectambonites segmentum (Angelin), var. nov. woodlandensis. 

 (Plate XIV, figs. 36-41.) 



1883. Leptama segmentum, Angelin, Davidson (pars), Mon. Brit. Foss. Brack., vol. v, Silur. Suppl., 

 p. 227. 



Shell small, short, swollen, rounded, subtriangular to semicircular, strongly 

 concavo-convex ; cardinal angles pointed, acute, depressed, more or less produced 

 into very short semicylindrical ears. Pedicle-valve semiglobose, much inflated, 

 with very small depressed pointed lateral angles ; beak swollen, much incurved, and 

 overhanging ; hinge-area r arrow, lying in plane of valve. Brachial valve strongly 

 concave ; hinge-area at right angles. Surface of pedicle-valve with 3-5 primary 

 radii, of which the middle 2 or 3 are most pronounced ; interspaces with very 

 fine delicate or indistinct striae. Interior unknown. 



Dimensions. — Length, 5 '5-6 mm. ; width, 8 mm. 



Horizon. — Saugh Hill Group. 



Locality. — Woodland Point. 



Remarks. — Davidson labelled some of these shells L. quinquecostata ; the 

 ribbing, indeed, bears much resemblance, but the contour and shape more resemble 

 PI. Etheridgei. The shell is generally more inflated and globose, the cardinal 

 angles smaller, more pointed, and semicylindrical, and the beak more swollen 

 and incurved than in the Dudley examples of PI. segmentum. 

 * Davidson, op. cit., vol. iii, p. 321, pi. xlviii, figs. 28-30. 



