ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 953 



Genus Whitfieldella, Hall and Clarke. 



Whitfieldella angustifrons (M'Coy). 

 (Plate XXIV, fig. 50.) 



1851. Hemithyris angustifrons, M'Coy, Ann. Mag. Nat. Hist., ser. 2, vol. viii, p. 391. 



1851. Terebratula angustifrons, Salter, Quart. Journ. Geol. Soc, vol. vii, pi. 9, fig. 10. 



1852. Hemithyris angustifrons, M'Coy, Syn. Brit. Pal. Foss. Woodw. Mus., p. 199, pi. in, figs. 6-8. 

 1866. Meristella angustifrons, Davidson, Mon. Brit. Foss. Brack., vol. iii, pt. vii, p. Ill, pi. x, 



figs. 21-27. 

 1885. Meristella ? angustifrons, Davidson, op. cit., vol. v, Situr. Suppl., p. 133, pi. viii, fig. 1 ; pJ224. 



M'Coy's type-specimens came from the " sandstone of Dalquorhan," Mulloch 

 Quarry, and all Davidson's figured specimens came from Mulloch Hill, but he also 

 records the species from the " head of Thraive Glen, Auld Thorns, and Thraive." I 

 have only seen specimens from Mulloch Hill, Auld Thorns, and Craigens. The 

 internal characters are excellently displayed in internal casts, and were partly 

 described by M'Coy and Davidson. It should be mentioned that the hinge-plate is 

 divided into a pair of triangular portions by a narrow median slit ; the crura seem to 

 be short and sharply pointed, and there is no definite median septum, but only a thin 

 weak low median ridge. The pedicle-valve shows a circular apical foramen with the 

 deltidium below it, and the diductor scars are more marked and flabelliform than 

 Davidson represented in his fig. 26a, pi. x, while there is only a narrow low median 

 ridge which is not continued in front of the diductors ; the beak also has the shell 

 thickened internally. We may especially compare this species with Whitfieldella 

 cylindrica, (Hall), # of the Clinton and Niagara Formations. 



Horizon. — Mulloch Hill Group. 



Localities. — Mulloch Hill, Auld Thorns, Craigens. 



Whitfieldella nitida (Hall), var. ? 

 (Plate XXIV, fig. 51.) 

 There are several specimens of a broad flattened subcircular shell associated with 

 Whitfieldella angustifrons at Mulloch Hill which seem closely to resemble Whit- 

 fieldella nitida, var. oblata, Hall,t Whitf. intermedia, Hall, J and Whitf oblata, Hall.§ 

 One interior of a shell of similar shape and external appearance shows the spiral cones 

 facing outwards, as is typical in the genus, and they are composed of 6-8 turns, 

 with a pair of parallel closely placed supporting bands. The broadly obovate shape 

 widening towards the anterior end and generally more flattened towards the margins, 

 distinguishes this shell from the much commoner Whitf. angustifrons, and it does 

 not seem possible to regard it as only a variety of the latter. The anterior margin 

 has a very broad scarcely perceptible median sinuation. 



* Hall, Palseont. N.Y., ii, 1852, p. 76, pi. 24, fig. 2 ; Hall and Clarke, op. cit., Bracb., ii, p. 58, pi. xl, 

 figs. 16-22. 



t Hall, Palseont. N.Y. ii, 1852, p. 269, pi. 55, fig. 2. J Ibid., p. 77, pi. 24, figs. 3, 4, ?6. 



§ Ibid., p. 9, pi. 4, figs. 4, 5. 



