530 • DR WHEELTON HIND ON 



Edmondia silurica, sp. nov. (PL V., figs. 2-4.) 



Specific Characters. — Shell triangularly subcircular, moderately gibbose, posterior 

 portion a little larger than the anterior. The anterior inferior and posterior margins form 

 an almost circular curve. Hinge line arched. Umbones small, subcentral, elevated, 

 incurved. The valve is regularly tumid from above downwards and before backwards. 



Interior. — Hinge plate bears an internal, semicircular plate which leaves an impres- 

 sion in casts. Adductor muscle scars normal. 



Exterior. — The surface is ornamented by numerous (14) almost equidistant, raised, 

 narrow concentric ridges, separated by broader shallow grooves. 



Dimensions. — Fig. 3, PI. V., a left valve, measures : antero- posteriorly, 7 mm. ; 

 dorso-ventrally, 5 mm. 



Locality. — Scotland : Llandeilo beds, Dowhill, Ardmillan. 



Observations. — Fortunately, one specimen showed the cast of the hinge plate, making 

 the generic relationship clear. This species has a marked similarity to Edmondia 

 Maccoyi of the Carboniferous rocks, but the latter is somewhat more quadrate in form. 

 The ornament is very similar. E. silurica seems to be not uncommon in the Gray 

 Collection. 



Edmondia simplex, sp. nov. (PI. V., figs. 5-7 a.) 



Specific characters. — Shell small, ovate, moderately convex, inequilateral. The 

 anterior end short and compressed, margin regularly rounded. The inferior margin 

 broadly convex, the posterior almost elliptical. The hinge line very slightly arcuate. 

 Its umbones are erect, pointed, directed slightly forwards, not contiguous, and placed at 

 the junction of the anterior and middle thirds of the hinge plate. The dorsal slope is 

 convex, gradually compressed. There is an obscure oblique ridge and sulcus which 

 extends from the umbo to the lower border in the anterior part of the valve. 



Interior. — Hinge plate edentulous. The anterior adductor muscle scar is small, and 

 placed immediately within the anterior superior angle, and is separated from the cavity 

 of the umbo by a thick ridge of shell. 



Exterior. — The surface is ornamented by fine, close, concentric lines and striae of 

 growth, interrupted in front as they pass over the oblique groove. 



Dimensions. — Fig. 7, PI. V., measures: antero-posteriorly, 17 mm.; dorso- 

 ventrally, 13 mm. ; from side to side, 7 mm. 



Locality. — The Llandeilo series of Ardmillan ; Shalloch Mill, Middle Bala ; Mulloch 

 Hill, Lower Llandovery ; ? Woodland Point, Middle Llandovery. 



Observations. — I have referred a number of specimens from somewhat dilf'erent 

 horizons to this species. The best material consists of two specimens from Ardmillan, 

 one of which is a cast of the interior. The valves were close, without escutcheon or 



