ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE GIRVAN DISTRICT. 891 



cardinal margins is given as the main distinction from Rafinesquina. The genus, 

 however, certainly occurs in the British Ordovician, and probably is represented by 

 more than one subgenus. But the groups of OrdoAdcian species are not as yet 

 firmly enough established to warrant distinctive names. 



Stropheodonta arenacea (Salter MS.). 

 (Plate XVI, fig. 19.) 



1865. Strophomena arenacea, Salter, Cat. Mux. Pract. Geol., p. 36. 



1870. Strophomena arenacea, Salter, Davidson, Mon. Brit. Foss. Brack., vol. iii, pt. vii, p. 296, 



pt. xlii, figs. 6-8. 

 1883. Strophomena arenacea, Salter, Davidson, ibid., vol. v, Silur. Suppl., p. 197, pi. xvi, figs. 3, 4, 5 



(Ifig. 2). 



Davidson recorded this species from Camregan Wood and Woodland Point, but 

 the specimen which he figured from the latter locality is doubtful, and there are 

 also certain specimens in Mrs Gray's collection from Camregan Wood which he 

 labelled Str. compressa, but they must certainly be referred to Str. arenacea. The 

 following additional details of internal structure may be gathered from these specimens, 

 two of the internal casts of the brachial valve being well preserved. The hinge-line 

 is finely denticulate, the cardinal process is prominent and divided into two triangular 

 lobes diverging and increasing in height anteriorly and with the posterior sloping 

 face of each lobe grooved ; the hinge-plate is thickened, elongated, diamond-shaped, 

 pointed in front, and it separates posteriorly the elongated parallel adductors which 

 are ill defined in front ; the crural plates are short, and make an angle of about 30° 

 with the hinge-line. These shells have a subquadrate shape like Davidson's figured 

 specimens from Gunwich Mill and Huntley Hill (op. cit., vol. iii, p. 297, pi. xlii, 

 figs. 7, 8) and are not transverse like the first figured example (fig. 6) from Norbury. 

 Davidson was of the opinion that two species had been included by Salter under 

 this name, and this seems to be very probable. 



Horizons. — (l) Camregan Group ; (2) Saugh Hill Group. 



Localities. — (l) Camregan Wood ; (2) Woodland Point. 



Stropheodonta corrugatella (Davidson). 

 (Plate XVI, fig. 20.) 



1870. Strophomena corrugatella, Davidson (pars), Mon. Brit. Foss. Brack., vol. iii, p. 301, pi. xli. 

 figs. 8-11 (non figs. 12-14, nee Suppl., pi. xv, figs. 23-26). 



The true Stroph. corrugatella seems to occur in the Starfish Bed, and this is 

 approximately on the same horizon as the Desertcreat, Keisley, and Kildare beds in 

 which it is well known. It agrees fairly well with the type of this species, Orthis 

 corrugata of Portlock,* from Desertcreat, but the transverse pittings in the inter- 

 spaces are not clearly crescentic, and they do not seem so large or so generally developed 



* Poktlock, Geol. Rep. Londond., p. 450, pi. xxxii, figs. 17, 18. 

 TRANS. ROY SOC. ED1N., VOL. LI, PART IV (NO. 26). 128 



