ORDOVICTAN AND SILURIAN BRACHIOPODA OF THE GTRVAN DISTRICT. 867 



resemble the form from Grangegeeth, Co. Meath, figured by Davidson (op. cit., iii, 

 p. xlii, fig. 3) ; the interior of the brachial valve is well shown, and is identical in 

 character with the latter (figs. 3a, 3b). The disc is about three-fourths the length 

 of the shell and is as long as wide ; the rugae number 16-18 and are regularly con- 

 centric and continuous right across the disc, meeting the hinge-line nearly at right 

 angles, whereas in the common Balclatchie form there are only 3-7 rugse developed 

 near the lateral angles, and meeting the hinge-line at an acute angle but continued 

 likewise across the disc. 



Dimensions. — Length, 20 mm. ; width, 26 mm. 



Horizon. — Balclatchie Group. 



Localities. — Ardmillan, ? Balclatchie. 



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



(Plate XII, figs. 2, 3.) 



There is a large imperfectly known shell occurring in the Balclatchie Beds and 

 represented by only about half a dozen poor specimens in Mrs Gray's collection 

 which seems to be a definite variety of R. deltoidea distinct from that termed multi- 

 corrugata. The general shape and ornamentation are those of R. deltoidea, but over 

 the whole disc, which extends about half the length of the shell, there are 20-25 fine 

 close irregularly undulating concentric rugae, mostly broken and non-continuous. 

 This is a marked feature, and more recalls some specimens of Leptwna rhomboidalis 

 than the usual form of R. deltoidea occurring on this horizon. 



Dimensions. — Width, 30-38 mm. 



Horizon. — Balclatchie Group. 



Locality. — Balclatchie. 



Rafinesquina (PlayfairiaVjfelix, sp. nov. 



(Plate XII, figs. 4-10.) 



Shell gently concavo-convex, flattened, with anterior margin very slightly bent 



down but not geniculated, transversely semicircular; widest along hinge-line; 



cardinal angles flattened, acutely pointed, produced into small pointed distinct ears. 



Pedicle-valve very slightly convex, more or less flattened, gently arched down near 



margin ; beak small, sharp, pointed, slightly elevated, and projecting above hinge-line ; 



hinge-area narrow, striated from end to end ; teeth small, curved, elongated, nearly 



parallel to hinge-line ; interior with small transversely subcircular muscle-scar, about 



one-fourth the length of the valve, well defined at sides ; diductors subtriangular, 



slightly diverging anteriorly, and embracing narrow elongate adductor scar ; pair of 



narrow vascular trunks running forwards from diductors and breaking up into a few 



smaller vessels ; whole interior coarsely pustulate in radial lines. Brachial valve 



gently concave ; beak small, inconspicuous ; interior unknown. Exterior of valves 

 TRANS. ROY. SOC. EDIN., VOL. LI, PART IV (NO. 26). 125 



