ORDOAaCIAN AND SILURIAN BRACHTOPODA OF THE GIRYAN DISTRICT. 947 



Glassia obovata (Sowerby). 



1839. Atrypa obovata, Sowerby, in Murchison's Silurian System, p. 618, pi. viii, fig. 9. 



1866. Athyris obovata (Sowerby), Davidson, Mon. Brit. Foss. Brach., vol. iii, pt. vii, p. 121, pi. xii, 



fig. 19; pi. xiii, figs. 5, 5a. 

 1883. Glassia obovata (Sowerby), Davidson, ibid., vol. v, Silur. Suppl., pp. 116, 224, pi. viii, fig. 12. 



This species was described by Davidson from Penkill, and I have not seen any 

 examples from any other locality or horizon in the Girvan area. The internal 

 characters of this species have been described by means of specimens from the 

 Wenlock Shales of Shropshire (Davidson, op. cit., vol. v, p. 116, pi. vii, figs. 11-20), 

 and one internal cast from Penkill in Mrs Gray's collection shows the crural bands 

 in the brachial valve and the umbonal characters of the other valve. 



Horizon. — Penkill Group. 



Locality. — Penkill. 



Genus Clintonella, Hall and Clarke. 



Clintonella cf. vagdbunda, Hall and Clarke. 



(Plate XXIV, fig. 32.) 



Shell regularly oval. Brachial valve flattened, marked by deep well-marked 

 wide median sinus extending from beak to margin, rapidly increasing in width 

 anteriorly, and with its floor occupied in anterior third by one simple gently rounded 

 low fold ; lateral lobes of shell with inner portion occupied by 3 straight subequal 

 narrow rounded closely placed ribs on each side of sinus, but outer posterior part of 

 lobes smooth and not ribbed ; beak low, inconspicuous. 



Dimensions. — Length, 3'4 mm. ; width, 2'8 mm. 



Horizon. — Saugh Hill Group. 



Locality. — Newlands. 



Remarks. — No species except Clintonella vagabunda, Hall and Clarke,* of the 

 Clinton Formation of the United States, appears to bear any resemblance to this 

 little shell, of which I know only one specimen in Mrs Gray's collection, represented 

 by an internal cast and the external impression of the same brachial valve. 



Genus Atrypa, Dalman. 

 Atrypa expansa, Lindstrom, var. 



A shell indistinguishable from the variety of A. expansa, with few ribs, which was 

 described by Lindstrom t from Dalecarlia, occurs at Shalloch Mill, but is rare. It is 

 closely allied to A. imbricata, Sow. 



Dimensions. — ^Length, 17 mm. ; width, 19 mm. 



* Hall and Clarke, op. cit, Brach., ii, p. 159, pi. Iii, figs. 1-11. 

 t Lindstrom, Fragm. Silur., p. 22, t. xii, figs. 17-19. 

 TRANS. ROY. SOC. EDTN., VOL. LI, PART IV NO. 26). 135 



