ORDOVICTAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 887 



iii, pi. xlviii, fig. 9b) in a pedicle-valve from the Pentland Hills. The others are fairly 

 distinct 'varieties. The typical form occurs at Woodland Point, and is distinguished 

 externally from the Mulloch Hill variety by its much more numerous radii. The 

 transversely elongated form from Woodland Point has fewer radii than the type, as 

 well as other differences, and never attains such large dimensions. 



Dimensions (typical form). — Length, 15-17 mm. ; width, 21-23 mm. 



Horizon. — Saugh Hill Group. 



Localities. — Woodland Point, Newlands. 



Plectambonites transversalis (Dalman), var. Duvali, Davidson. 

 (Plate XV, figs. 37-40.) 

 1847. Leptxna Duvalii, Davidson, Geo!. Journ. London, vol. i, p. 58, pi. xii, figs. 17-19. 



The transverse shells from Woodland Point, with more or less produced sub- 

 cylindrical pointed cardinal angles and fusiform shape, do not appear to be sharply 

 separable from the typical PI. transversalis which occurs on the same horizon 

 associated with them. But the extreme forms are sufficiently distinct, and to these 

 Davidson * applied the varietal name Duvali. With regard to external characters, 

 it may be remarked that the Girvan examples of this variety sometimes have the 

 interspaces between the primary radii slightly concave and depressed, especially near 

 the margin, and the primary radii near the middle of the pedicle-valve are often larger 

 and thicker than the others. In the interior of one pedicle-valve it may be observed 

 that there is a pair of gently arched strong vascular trunks which cross obliquely the 

 elongated faintly impressed divergent diductor scars and extend about one-third to 

 one-half the length of the valve before dividing into two or more strongly divergent 

 small branches. An oval adductor scar lies in the fork of the diductors. The 

 lateral portions and cardinal region are coarsely pustulate, but elsewhere finer and 

 smaller papilhe are developed in radial lines. The brachial valve possesses internally 

 a pair of subparallel oval or linguiform compound muscle-scars, about half the length 

 of the valve, each with strongly raised inner edges and divided longitudinally into 

 anterior and posterior adductors ; a prominent median septum shorter than the scars 

 is developed in the space between them. 



Horizon. — Saugh Hill Group. 



Localities. — Woodland Point, Newlands. 



Plectambonites transversalis (Dalman), var. nov. mullochensis. 



(Plate XV, figs. 41, 42; Plate XVI, figs. 1,2.) 



Shell transversely subtriangular to subsemicircular, concavo-convex ; cardinal 



angles pointed at 45°-60°, not alate nor produced ; cardinal line minutely denticulate 



for more than three-fourths its length on each side of beak, with 20-25 small teeth. 



* Davidson, op. cit, vol. iii, p. 318, pi. xlviii, figs. 4, 5. 



