EDMONDIA UNIONIFORMIS. 293 



slope, remote from the margin. The hinge-plate is edentulous, with a deep, thick, 

 curved vertical ridge of shell, and the flat expanded ossicle seen as a groove in 

 casts. Pallial line entire. 



Exterior. — The surface is ornamented with concentric lines and fine ridges, 

 very conspicuous in the anterior part of the shell. Posteriorly the shell is almost 

 smooth, but the linear ridges are more apparent again near their termination as 

 they curve round to pass into the superior border. Shell moderately thick. 



Dimensions. — Fig. 1, PI. XXVIII, the type of Isocardia unioniformis, Phillips, 

 measures — 



Antero-posteriorly . . . .49 mm. 



Dorso-ventrally . . . .36 mm. 



Laterally . . . . .26 mm. 



Localities. — England : the Carboniferous Limestone of Bolland, Withgill, and 

 Hill Bolton, Yorkshire ; Castleton, Thorpe Cloud, Derbyshire ; the Redesdale 

 Ironstone shale and limestone of Lowick and the Coombs, Northumberland. The 

 Upper Carboniferous Limestone of Poolvash, Isle of Man. Scotland : The Lower 

 Limestone series of Beith ; Hind og glen, Dairy ; Inverteil, Kirkcaldy ; Tweeden 

 burn, Cement stone Series, Roxburgh ; Encrinite-bed, St. Andrews, Fife. Ire- 

 land : Rochfort Lodge, Bundoran, co. Donegal; Tomcleely, Ballygarrane, and 

 Ballyshonickbane, co. Limerick. 



Observations. — This species was described by Phillips under the genus Iso- 

 cardia, and de Koninck subsequently thought that he founded the genus Edmondia 

 on Belgian shells which were identical with the British species. This, however, 

 was not the case, for, as M'Coy pointed out, the Belgian examples were "too 

 nearly orbicular, the anterior end being too long and the ventral margin too much 

 arched to agree with the present species." The same criticism can be applied to 

 the shells referred to Edmondia unioniformis in de Koninck's later work, which 

 certainly do not belong to that species. The shells named by de Koninck E. 

 prselata belong, I think, undoubtedly to the species under discussion, probably also 

 E. decorata and E. prsecox. Phillips makes the following statement: — " Surface 

 wrinkled on the posterior slope," the accuracy of which M'Coy questioned I 

 think that this mistake arose from the absence of the shell in the anterior portion 

 of the type specimen ; for on reference to fig. 1, PI. XXVIII, it will be seen that 

 the posterior portion of the shell has its markings more apparent. 



M'Coy describes the " anterior lunette" as " very large, oval, deep; " but in 

 common with all other members of the family there is no lunule, the concentric lines 

 of growth curving round the antero-superior angle to terminate in the hinge-line. 



I am of opinion that most of the species in lists named E. unioniformis are 

 erroneously referred to this species. I have been able to find only very few 

 examples which agree in character with the type. 



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