8f>6 DR F. R, C. REED ON THE 



collector of fossils in the Girvan area. I have not identified with certainty any 

 representative of this variety from the Balclatchie Group. 



Subgenus nov. playfairia. 



Definition. — Shell concavo-convex, generally geniculated. Interior of pedicle- 

 Naive with small subcircular or subpentagonal muscle-scar, about one-fourth the 

 length of the valve ; vascular markings and pustules generally present. Brachial 

 valve with internal characters closely resembling Leptsena. 



Type : Leptsena deltoidea, Conrad. 



Remarks. — This subgenus is distinguished from the typical Rafinesquina by the 

 smallness of the diductors in the pedicle-valve and by the internal characters of the 

 brachial valve being almost identical with Leptsena (type L. rhomboidalis). The 

 general habit is also that of Leptsena. 



Rafinesquina {Playfairia) deltoidea (Conrad). 

 (Plate XI, figs. 21-30.) 



1839. Strophomena deltoidea, Conrad, 3rd Ann. Rep. New York Geol. Surv., p. 64. 

 1883. Strophomena deltoidea, Conrad, Davidson, Mon. Brit. Foss. Brach., vol. v, Silur. Suppl., p. 197, 

 pi. xv, figs. 16-22. 

 Non 1870. Strophomena deltoidea, Conrad, Davidson (pars), ibid., vol. iii, pi. xlii, figs. 3a, 36. 



This well-marked species, originally described from the -Trenton Limestone of 

 which it is a typical form, is abundant in the Balclatchie Group. The average size 

 of the specimens is only 10-12 mm. in width. The geniculation is not usually so 

 abrupt and angular as Davidson made it appear to be in his figures, nor is the disc 

 generally so flattened or defined. His figure also (op. cit., fig. 22) of the interior of a 

 brachial valve is misleading, for the muscle-scars are less definitely circumscribed and 

 of a different shape than represented ; the anterior pair forms a long subrhomboida! 

 scar much longer and narrower than the posterior pair, which are shorter, trans- 

 verse, laterally extended, radially ridged and flabelliform rather than subcircular. 

 Examples of this species from the Stinchar Limestone are less common than from 

 the Balclatchie Beds and are usually of a larger size, some being as much as 25 mm. 

 in width ; the disc also is generally flatter. 



Horizons. — (l) Stinchar Limestone Group; (2) Balclatchie Group. 



Localities. — (l) Craighead; (2) Ardmillan, Dow Hill, Balclatchie. 



Rafinesquina (Playfairia) deltoidea (Conrad), var. nov. multicorrugata. 



(Plate XI, fig. 31 ; Plate XII, fig. 1.) 



Cf. 187(J. Strophomena deltoidea, Davidson, Mon. Brit. Foss. Brach., vol. iii, pt. vii, p. 292, pi. xlii, 

 figs. 3, Za-h. 



Some specimens from Ardmillan in Mrs Gray's collection are decidedly different 

 from the common type of R. deltoidea occurring in the Balclatchie Beds, and closely 



