THE LAMELLIBRANCHS OF THE SILURIAN ROCKS OF GIRVAN. 531 



lunule, and apparently edentulous, with a thickened hinge plate, and on these grounds 

 I have referred the shells to Edmondia. The absence of any ridges or external moulding, 

 and the simple character, agree with Edmondia rather than with any other genus. 



Edmondia antiqua, sp. nov. (PL V., figs. 8-10.) 



Specific Characters. — Shell small, transversal, oval, regularly gibbose. The anterior 

 end rounded, the inferior margin broadly convex, the posterior rounded. The hinge 

 line gently arcuate. The umbones small, blunt, slightly raised, incurved, placed at the 

 junction of the anterior and middle thirds of the hinge line. 



The valve is without ridge, and is regularly convex from above downwards and 

 before backwards. 



Interior. — The hinge plate is normal ; a groove is seen in casts for the characteristic 

 umbonal plate, long and deep ; anterior adductor muscle scar large, deep, and round ; 

 posterior shallow and large, both normal in position. 



Exterior. — The surface is ornamented with regular concentric rugse and undulations 

 of growth. 



Dimensions. — Fig. 8, PL V., an internal cast of the right valve, measures : antero- 

 posterior^, 13 mm. ; dorso-ventrally, 8 mm. ; elevation of valve, 3 mm. 



Localities. — Llandeilo beds of Ardmillan, Dowhill, and Craighead. 



Observations. — Five specimens in the collection I refer to this species. One of 

 them (PL V., fig. 8) is a cast of the interior, which shows the internal characters of 

 Edmondia. The internal plate characteristic of the genus was well developed in the 

 Ordovician representatives of the genus. The species has the simple, regular, featureless 

 characters of many of the species of the genus. 



Genus Slava, Barrande, 1881. 



Gardiola, Sowerby, 1839, Sil. Syst., p. 617. 



Slam, Barrande, 1881, Syst. Sil. de la Boheme, vol. vi p. 154. 



Tiariconcha, Freeh, 1891, Devon., S. 251. 



,, Beushausen, 1S95, Die Lamell. ties rheinischen Devon., p. 318 (Abh. Konigl. Preuss 



Geol. Landesanstalt, N.F., Heft xvii.). 



Generic Characters. — Shell ovate, acute. Umbones acute, slightly prosogyrous. 

 Hinge line short and arched. Ornament consists of flat, broad, concentric, convex folds 

 and grooves in the young part of the shell, but of fine radiating lines in the lower or 

 older posterior. 



Observations. — Frech separated the group of Cardiola fibrosa, Sow., under the 

 name of Tiariconcha (supra cit.), and referred certain Devonian forms to that genus. 

 Beushausen followed him, and described three species (op. supra cit.). Reference to 



