ORDOVICIAN AND SILURIAN* BRACHIOPODA OF THE GIRVAN DISTRICT. 821 



Orbiculoidea stincharensis, sp. nov. 

 (Plate IV, figs. 21-24.) 



1883. Discma perrugata (M'Coy), Davidson, Mon. Brit. Foss. Brack., vol. v, Silur. Suppl., pp. 210, 

 224, pi. xvii, fig. 47. 



Shell slightly oval or elliptical, longer than wide. Pedicle-valve low conical, more 

 or less flattened ; apex subcentral, rather nearer posterior than anterior end ; interior 

 with pedicle-tube extending about half the distance from centre to margin. Brachial 

 valve with apex more excentric, situated about two-fifths to one-third of the diameter 

 from posterior margin. Surface covered with coarse rounded low concentric ridges. 



Dimensions. — Length, 7'5 mm. ; width, G'5 mm. 



Horizon. — Stinchar Limestone Group. 



Locality. — Craighead . 



Remarks. — The oval shape of the shell, the shorter pedicle-tube, and the coarser 

 and fewer concentric ridges distinguish this form from the other Girvan species. 

 It appears to resemble 0. lamellosa, Hall, # from the Trenton Formation, but has 

 more rounded concentric ridges. 



Subgenus schizotreta, Kutorga. 



Orbiculoidea (Schizotreta ?) Forbesi, Davidson. 



(Plate IV, fig. 25.) 



1848. Orbicula Forbesi, Davidson, Bull. Soc. Geol. France, siv. 2, vol. v, p. 334, pi. iii, fig. 45. 



1866. Orbiculoidea Forbesi, Davidson, Mon. Brit. Foss. Brack., vol. iii, pt. vii, p. 73, pi. vii, figs. 14-18. 



1883. Orbiculoidea Forbesi, Davidson, Mon. Brit. Foss. Brack., vol. v, Silur. Suppl., p. 224. 



The specimens attributable to O. Forbesi from Woodland Point are broken or 

 poorly preserved, and the internal and apical characters are not clearly recognisable. 

 One pedicle-valve is circular or subcircular in shape, and shows minute transverse 

 striae in the rather broad grooves between the narrow concentric ridges on the surface. 

 The brachial valves have a more excentric apex, and are oval or rather narrower 

 posteriorly, as Davidson mentions. The Niagaran species, Orbic. (Schizotreta) 

 tenuilamellata (Hall) t is probably closely allied. 



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



Localities.— (\) Woodland Point ; (2) Mulloch Hill. 



" Orbicula oblongata." 



The specimens attributed by Davidson % to "Orbicula" [Discina] oblongata, 



Portlock,§ and described as Discina oblongata from the Balclatchie Beds, do not 



appear to be brachiopods at all. Only the so-called pedicle-valve has been found, and 



Davidson himself remarked (op. cit., p. 6G) that no "lower" [brachial] valve was 



* Hall, Palxont. New York, vol. i, 1847, p. 99, pi. 30, fig. 10. 

 t Hall, Palxont. New York, vol. ii, 1852, p. 250, pi. 53, fig. 3. 



I Davidson, Mon. Brit. Foss. Brack., vol. iii, pt. vii, p. 66, pi. vii, figs. 4, 5? ; ibid., Suppl., v, p. 209, pi. xvii, 

 figs. 13-46. § Portlock, Rep. Geol. Londond. (1843), p. 445, pi. xxxii, fig. 13. 



