276 CARBONIFEROUS LAMELLIBRANCHIATA. 



seem, however, to form well-defined intermediate stages between C. oblonga and 

 the species under description. M'Coy soon changed his view as to the generic 

 character of this species, for he relegated it to Edmondia, with which it has 

 certain resemblances ; and it seems, indeed, to be a link between that genus and 

 Cardiomorpha. 



De Koninck figures several shells {op. cit.) under the names Pachydomus 

 Egertoni, P. depressus, and P. MacCoyi, which I am disposed to regard as the 

 same species. Curiously enough, the shells which he refers to M'Coy's species 

 are less like the type than either of the others, being less orbicular and more 

 transverse ; but such a variety occurs in Ireland, an example of which I figure, 

 PI. XXIV, fig. 1. The first and third of these are stated to occur in etage II, 

 Pauquys, the second in etage I, Vise ; which to some extent accounts for the 

 number of species. Both M'Coy and de Koninck describe this species as 

 possessing a lunette, but this is a mistake. In M'Coy's type specimen the shell 

 is absent at the antero-superior part, and the groove for the hinge-plate in the 

 cast has been perhaps mistaken for a lunule ; but an examination of Figs. 1 and 3 a, 

 PI. XXV, shows that, in common with all other species of the family, P. Egertoni 

 has no lunule. I have no hesitation in referring the Cardium orbiculare and 

 Mactra incrassata of M'Coy to this species, the type specimens of which I 

 figured, PI. XXV, fig. 2. The latter shows a series of equidistant, deep, con- 

 centric grooves in the cast, which has been mistaken by M'Coy for the external 

 surface, although a portion of the shell is preserved lower down. This character 

 is also present in Fig. 1, PI. XXV, a specimen from Nanteenan, co. Limerick, 

 in the collection of the Geological Survey of Ireland, which fortunately has 

 the shell preserved on the other valve. This character is an approach towards 

 the concentric markings of C. ventricosa and C. corrugata, and is another 

 character showing the affinity of the species to the genus Cardiomorpha rather 

 than to Edmondia . 



The original type of Cardium orbiculare is extant in the Griffith Collection of 

 the Museum of Science and Art, Dublin, and it is figured in Fig. 2, PI. XXIV. 

 Both valves are preserved with a portion of the shell, but they have slipped some- 

 what one on another. This is a younger example than the type of C. Egertoni, 

 and consequently the shell is not so thick. 



C. Egertoni is quoted by Messrs. Young and Armstrong in their List of 

 Carboniferous Lamellibranchs from the West of Scotland under the generic name 

 " Edmondia." The shells which I find with this name attached in Scottish 

 collections are Edmondia senilis, Phillips, sp., and I have not yet come across this 

 species in the Carboniferous series of the West of Scotland. They also mention 

 Mactra ? incrassata as occurring at Craigenglen, but I have not seen any shell 

 that I can identify as the species. 



