ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 815 



them together in his list of references to the species. Some of these Girvan specimens 

 were labelled by Davidson Siphonotreta micula, M'Coy, but they do not possess the 

 shape or characters of that species, being subcircular in outline, and having irregular 

 sublamellose finely fimbriated concentric striae ; the beak also is intra-marginal, and 

 seems to form the apex of a low cone. In size they average 3 mm. in diameter or 

 less. A. granulata, Linnarss., is taken by Walcott as the type of his subgenus 

 Redlichella (op. cit., p. 662). 



Horizon. — Balclatchie Group. 



Locality. — Balclatchie. 



Genus Acrotreta, Kutorga. 

 " Acrotreta costata," Davidson. 



1883. Acrotreta 1 costata, Davidson, Mon. Brit. Foss. Brack., vol. v, Silur. Suppl., p. 213, pi. xvi, 

 fig. 24. 



The one small specimen on which this species is based is very imperfect, and 

 Davidson's figure is a highly imaginative restoration, unless the specimen has sub- 

 sequently been much injured, which does not seem to have been the case. The shell 

 may belong either to the genus Conotreta or Acrotreta, but the " radial ribs " which 

 are now visible seem to be only the imperfect cast of the posterior face of the pedicle- 

 valve showing the pedicle-groove and edges of the false-area. But the specimen is 

 too poorly preserved and too fragmentary for a satisfactory determination. Walcott * 

 says : ' The description and figures suggest a genus allied to Cyrtia, Hall and Clarke, 

 of the Silurian " ; but, as stated above, Davidson's figures are untrustworthy. 



Horizon. — Balclatchie Group. 



Locality. — Balclatchie. 



Acrotreta Nicholsoni, Davidson ? 



1 1868. Acrotreta t Nicholsoni, Davidson, Geol. Mag., vol. v, p. 313, pi. xvi, figs. 14-16. 

 1871. Acrotreta ? Nicholsoni, Davidson (pars), Mon. Brit. Foss. Brack., vol. iii, pt. vii, p. 343, pi. xlix, 

 figs. 36, 37, 40 (non figs. 38, 39). 

 Non 1883. Acrotreta Nicholsoni, Davidson, op. cit., vol. v, Silur. Suppl., p. 213, pi. xvi, figs. 21-23. 



1912. Acrotreta Nicholsoni, Walcott (pars), Camb. Brack. (Mon. U.S. Geol. Surv., vol. li, 1912), 

 p. 696, pi. Ixxiii, figs. 1, lc, Id, Ih, li, Ik (non figs, la, lb, le, 1/, lg). 



In describing the new species Micromitra Davidsoni it has been mentioned above 

 that the type of A. Nicholsoni came from Dobbs' Linn, Moffat. Lapworth f only 

 records the latter from the zone of Dicrano. Clingani in that region. The Girvan 

 specimens referred by Davidson to this Moffat species cannot be retained in it or in 

 the same genus, though Walcott has adopted Davidson's conclusions and figures. An 

 examination of the figured specimens shows that the drawings are incorrect and mis- 

 leading. The median groove from the apical foramen of the pedicle-valve to the 



* Walcott, Camb. Brack. (Mon. U.S. Geol. Surv., vol. li, 1912), p. 674. 

 t Lapworth, Quart. Journ. Geol. Soc, vol. xxxiv, 1878, pp. 313, 331. 



