174 Proceedings of the Royal Physical Society. 



some of the latter the minute lateral spines are well jDre- 

 served. 



Loc. and Horizon. — Balcletchie, sonth-east of Girvan, in 

 rocks of Silurian age ; position uncertain. 



CLASS BRACHIOPODA— TRETENTERATA. 

 Genus Discina — Lamar ch, 1819. 



(Hist. Anim. sans Verteb,, vi,, pt. 1, p. 236.) 



Discina PortlocJci, Geinitz (?). 



Orhicida PortlocJd, Geinitz. Dei Graptolithen, etc., 1852, 

 p. 26, t. 1, 1 31 and 32. 



Ohs. — Mrs Gray informs me that these little shells were so 

 named by Mr C. Lapworth, F.G.S. They certainly bear a con- 

 siderable resemblance to Geinitz's iigure, especially his Fig. 31. 

 They have the almost marginal umbo, and behind it the " last- 

 shaped " elevation mentioned by Geinitz. They are oval- 

 circular, and the lines of growth are both close and well 

 marked. Geinitz considered his shell identical with Orlicula 

 Immgata, Portlock (Geol. Eeport on Londonderry, p. 445, 

 t. 32, f. 11 and 12), but not of MUnster. Now, 0. laevigata, 

 Portlock, is a much larger and more circular shell, and is 

 placed by Mr Davidson as a synonym of Discina oblongata, 

 Portlock (Mon. Brit. Sil. Brachiop., p. 66). The whole subject 

 requires investigation. 



Loc. — Balcletchie, south-east of Girvan, in rocks of Silurian 

 age ; j)osition uncertain. 



Gen us Acrotreta —KiUorga. 

 Acrotreta {?) Nicholsoni, Davidson (?). 



A. (?) Nicholsoni, Dav. Mon. Brit. Sil. Brachiopoda, p. 343, 

 t. 49, f. 36-40. 



Ohs. — This little shell has been noticed hitherto from the 

 Upper Llandeilo Graptolite shales near Moff'at. Mrs Gray has 

 three specimens bearing this name, which appear to possess 

 the peculiar hinge structure described by Mr Davidson, 

 although they are more conical than represented in the figures 

 quoted above. 



