ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 863 



what irregular in size in these specimens, but such is also sometimes the case in 

 English examples of the species. The original typical Shropshire specimens re- 

 figured by Davidson* from Acton Scott have no alation of the cardinal angles, and 

 such is also. the case with those from Girvan. 



Horizon. — Stinchar Limestone Group. 



Locality. — Craighead. 



Genus uncertain. 



Orthis ? nina, Davidson. 



(Plate XI, figs. 8-12.) 



1883. Orthis nina, Davidson, Mon. Brit. Foss. Brack., vol. v, Silur. Suppt.,'p. 177, pi. xiii, fig. 11. 



Shell small, semielliptical, plano-convex ; hinge-line equal to maximum width ; 

 cardinal angles rectangular. Pedicle-valve (?) low, subconical, w r ith broad weak median 

 sinus ; beak pointed, small, forming apex of cone, not elevated nor incurved ; hinge- 

 area triangular, nearly at right angles to plane of valve. Brachial valve (?) gently 

 convex ; beak elevated, slightly swollen, and incurved ; hinge-area narrow. Surface 

 of valve ornamented with about 50 fine closely placed straight ribs, of which every 

 third or fifth one (particularly in the middle of the pedicle-valve) is rather stronger. 



Dimensions. — Average width, 2-3 mm. 



Horizon. — Whitehouse Group. 



Locality. — Whitehouse Bay. 



Remarks. — This species was incorrectly and inadequately described by David- 

 son, so that the above revised description, based on the type specimens, is rendered 

 necessary. His figures were restorations, and are quite unlike both the specimens 

 labelled as figured and all the others named by him 0. nina. None are. well 

 preserved, and the species is altogether rather unsatisfactory, and it is doubtful 

 which is the pedicle-valve and which is the brachial. No specimens showing the 

 interior have been found. 



Genus Rafinesquina, Hall and Clarke, 



The genotype of Rafinesquina chosen by Hall and Clarke f is Leptaena 

 alternata, Conrad, which ranges from the Trenton to the Lorraine Groups in North 

 America. Some species, such as Leptaena deltoidea, Conrad, which were placed in 

 this genus by these authors, were specially mentioned as combining to some extent the 

 characters of Leptaena and Rafinesquina, and to this intermediate group some of the 

 Girvan species must be referred. A subgeneric name for this subordinate group is 

 desirable, and the name Playfairia is suggested, after the famous Edinburgh pro- 

 fessor, with L. deltoidea, Conrad, as the type (see p. 866). The generic position of 

 the new species described as Raf. brumalis and R. subarachnoidea is uncertain, as 



* Davidson, op. cit., vol. iii, pi. xxx, tigs. 11, 11a, b. 



f Hall and Clarke, op. cit., Brach., i, p. 281, pi. viii, figs. 6-11 {Raf. alternata). 



