EDMONDIA TRANSVERSA. 317 



Edmondia transversa, sp. nov. Plate XXXII, figs. 12 — 16. 



Specific Characters. — Shell of moderate size, transversely ovate, very inequi- 

 lateral, gibbose. The anterior end is extremely short and compressed, its border 

 curved and narrowed from above downwards. 



The inferior border is slightly convex and produced, passing into the posterior 

 border with an increased curvature. The posterior margin is bluntly rounded, 

 without any approach to angulation above or below. The hinge-line is arched in 

 front, but prolonged and almost straight behind. The umbones are gibbose, pro- 

 longed transversely, pointed, twisted inwards and forwards, contiguous, somewhat 

 raised, and situated quite in the anterior portion of the valve. 



The valves are evenly and convexly curved, and have a long dorsal slope, not 

 well marked off from the rest of the valve ; the greatest convexity is in front 

 and above the centre of the shell. 



Interior. — The anterior adductor scar is small and shallow, placed within the 

 antero-superior angle of the shell; the posterior scar is obsolete. The hinge- 

 plate in casts leaves two grooves parallel with the edge of the valve. The pallial 

 sinus is entire, and is represented by a well-marked groove not far from the 

 margin. The interior shows well-marked concentric grooves and sulci, crossed 

 by very fine decussating lines. 



Exterior. — The surface is ornamented with concentric grooves and sulci, more 

 or less regular, which are occupied by very fine concentric lines. Shell very 

 thin. 



Dimensions. — Fig. 12, PI. XXXII, measures — 



Antero-posteriorly . . . .35 mm. 



Dorso-ventrally . . . .24 mm. 



Laterally . . . . .12 mm. 



Localities. — Scotland : the Upper Limestone series of Garngad Road, Glas- 

 gow ; the Lower Limestone series of Beith and Auchenskeith, Ayrshire. 



Observations. — This species is associated with E. rudis in nodules in the 

 shales connected with the Beith Limestones in the Lower Limestone series of 

 Ayrshire, and though fairly plentiful, is not so frequent as the latter. E. trans- 

 versa seems to occupy a position midway between E. unioniformis and E. rudis. 

 It is more transverse and less deep in front than the latter, and more oblique than 

 either. At present I am unable to record the presence of this species, except at 

 the horizon noted above. 



It is probable that these are the shells referred to E. Egertoni in the catalogues 



41 



