ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 955 



Locality. — Mulloch Hill. 



Remarks. — Only three specimens of this shell are known, and they are in 

 Mrs Gray's collection ; one occurs as a good internal cast and external impression 

 of the pedicle-valve. In shape and external features it much resembles the shell 

 referred by Davidson * to Meristella Circe, Barrande, and its internal characters seem 

 to be those of Meristella. 



Meristella ? sp. 

 (Plate XXIV, fig. 55.) 



A few internal casts of small oval or subcircular smooth shells, measuring only 

 6-7 mm. in length, occur in Mrs Gray's collection from the Starfish Bed. They 

 show a pair of long gently arched dental plates at first converging slightly and then 

 diverging and enclosing between their anterior ends the beginning of the long 

 narrow deeply impressed and longitudinally striated diductor scar. The pedicle- 

 cavity also shows a strong muscle-scar. These features are typical of Meristella,^ 

 and to some extent recall M. crassa, Sowerby 4 from the Llandovery. Wiman § has 

 recorded a species of Meristella ? from the Leptsena Limestone which may be correlated 

 with the Starfish Bed, and Lindstrom || figures a shell which he refers to M. crassa 

 from the Leptsena Limestone and from a Lower Ordovician horizon. 



Horizon. — Drummuck Group (Starfish Bed). 



Locality. — Thraive Glen. 



Genus Ccblospira, Hall. 



Ccelospira hemispherica (Sowerby). 



1839. Atrypa hemispherica, Sowerby, in Murchison's Silur. Syst., p. 637, pi. xx, fig. 7. 



1866. Atrypa] hemispherica, Sowerby, Davidson, Mon. Brit. Foss. Brach., vol. iii, pfc. vii, pi. xiii, 



figs. 23-30 (? fig. 26). 

 1883. Leptoccelia hemispherica, Davidson (pars), op. cit., vol. v, Silur. Suppl., pp. 147, 225. 



Typical examples of this species occur at Camregan Wood and at Penkill. These 

 have the regular simple equidistant rounded ribs, as Davidson well depicts (op. cit., 

 supra) in his figures of May Hill specimens (fig. 23). He also figured examples from 

 Penkill (fig. 27), Penwhapple Glen (fig. 29), and Mulloch Hill (fig. 26), and from 

 Ardmillan (fig. 25).H But I have not seen any typical specimens from Mulloch Hill, 

 where the species C. scotica is found. The true C. hemispherica, sens, str., seems 

 confined to the Upper Llandovery Beds. Some examples from Penkill in Mrs Gray's 

 collection were named by Davidson Atrypa reticularis. 



Horizons. — (l) Camregan Group ; (2) Penkill Group. 



Localities. — (l) Camregan Wood ; (2) Penkill. 



* Davidson, op. cit., vol. iii, pt. vii, p. 116, pi. x, figs. 33-35 ; ibid., Suppl, v, p. 105, pi. iv, fig. 5. 



+ Hall and Clarke, op. cit, Brach., ii, p. 73, pi. xliv. j Davidson, op. cit., iii, p. 117, pi. xiii, figs. 1-3. 



§ Wiman, Arkiv for Zool., Bd. iii, No. 24, 1907, p. 6. 



|| Lindstrom, Fragm. Silurica, 1880, p. 21, t. xiii, figs. 4-8, 23-25. 



IT There must be some mistake in this locality, as no Llandovery Beds occur at Ardmillan. 



TRANS. ROY SOC. EDIN., VOL. LI, PART IV (NO. 26). 136 



