ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GTRVAN DISTRICT. 873 



Note. — -It has been hitherto held that the hinge-line of this species is not denti- 

 culated, but recently Chapman * has described a neanic specimen from the Silurian 

 of Victoria. Australia, which shows " fine but well-marked linear ridges normal to 

 the hinge-margin" along the cardinal line, " especially on the portions nearest to the 

 cardinal process of the opposed brachial valve." I have seen distinct signs of a similar 

 but more minute denticulation, extending apparently along the whole hinge-line in 

 some examples of var. £ from Bargany Pond Burn, and doubtful traces in some of 

 var. e from Woodland Point. 



Genus Leptella, Hall and Clarke. 



Leptella Grayse (Davidson). 



(Plate XIII, figs. 10-17.) 



1883. Leptcena Gray a, Davidson, Mon. Brit. Foss. Brack., vol. v, Silur. Suppl., p. 171, pi. xii, figs. 23-25. 

 1 1883. Leptcena Uandeiloensis, Davidson (pars), ibid., p. 171, pi. xii, figs. 27-29 (non fig. 26). 



Shell transversely subsemicircular to semielliptical or subtriangular, widest along 

 hinge-line ; concavo-convex ; cardinal angles rather less than right angles or rect- 

 angular. Pedicle-valve convex, subcarinate, most elevated along middle line, lateral 

 slopes more or less flattened ; beak small, pointed, not incurved ; hinge-area 

 triangular, at right angles to plane of valve, with triangular delthyrium. Brachial 

 valve slightly concave ; beak inconspicuous ; hinge-area very narrow. Interior of 

 pedicle-valve with small stout teeth and short rounded fiabelliform divergent 

 diductors about one-fifth the length of valve. Interior of brachial valve with 

 sharp prominent raised concentric ridge, emarginate in middle, situated at about 

 half the length of valve, bounding pair of large saucer-like areas in contact in 

 middle line along thin single or double median ridge joining emargination of 

 concentric ridge in front and here much elevated as a blunt spine ; saucer-shaped 

 areas radiately grooved and containing weakly impressed faint fiabelliform adductor 

 scars divisible into two contiguous radiating pairs. Surface of shell ornamented 

 with numerous straight low radiating subequal rounded thread-like radii numbering 

 100-120 on the margin, and increasing in number from the beak by frequent inter- 

 calation at irregular distances, some of the radii (primaries) being slightly stronger 

 than the others ; all crossed by fine concentric striation. 



Dimensions. — 



(Davidson's (Davidson's (Davidson's (Davidson's 



pi. xii, fig. 25.) pi. xii, fig. 27.) pi. xii, fig. 24.) pi. xii, fig. 23.) 



Length . . 14'0 20 14*5 13'0 8'0 mm. 



Width . . 22-5 27 25'0 18'5 10*0 mm. 



Horizons. — (l) Stinchar Limestone Group ; (2) Balclatchie Group. 

 Localities. — (l) Craighead, Doularg ? ; (2) Balclatchie (conglom.). 

 Remarks. — The species L. Grayse was based by Davidson on complete shells from 

 Craighead, but he only described the external characters, and apparently was not 



* Chapman, Proc. Roy. Soc. Victoria, vol. xxvi (N.S.), vol. i, pt. xvi, 1913, p. 102, pi. x, fig. 3. 



