CARDIOMORPHA VENTRICOSA. 267 



Interior. — The muscle-scars and pallial line are normal. The hinge has not 

 yet been exposed. 



Exterior. — The surface is ornamented by numerous almost microscopic lines of 

 growth, which are divided at irregular intervals, more frequent towards the lower 

 margin, by deep concentric grooves, the upper one of which is fairly broad from 

 above downwards ; but they diminish as they approach the margin. The finer 

 concentric lines are continued in the grooves as in other parts of the valve. 

 Shell thin. 



Dimensions. — Fig. 1, PL XXIII, a fairly perfect specimen in the collection of 

 Mr. J. Wright of Belfast, from the Limestone of Cork, measures — 



Antero-posteriorly. Dorso-ventrally. From side to side. 



33 mm. 38 mm. 37 mm. 



A more transverse example, 



PI. XXIII, fig. 3 . . 53 mm. 46 mm. 48 mm. 



Localities. — Ireland : the Carboniferous Limestone of Little Island, co. Cork. 



Observations. — This very distinct species Avas, M'Coy says (op. cit.), regarded 

 by him as a " monstrous variety of C. oblonga," but he erected the species on 

 becoming aware that examples were fairly common in the Limestone of Cork. 

 G. ventricosa differs very markedly from G. oblonga in its degree of gibbosity and 

 obliquity, and in its dorso-ventral diameter being longer than the antero-posterior, 

 whereas the opposite measurements obtain in G. oblonga. I have been able to 

 find the same characters in several young shells, which show the characteristic 

 linear sulci passing transversely across the shell, so typical of the species. One 

 of these, from Little Island, co. Cork, I figure, PI. XXIII, fig. 2. There is 

 another young specimen in the collection of the Geological Survey of Ireland. 

 M' Coy's original specimen is represented in the Griffith Collection in the Museum 

 of Science and Art, Dublin, by a plaster cast, but I am quite sure that the shell 

 from Mr. J. Wright's Collection, which I figure, PI. XXIII, fig. 1, was the type, 

 for it was originally part of the collection of the late Dr. Haines, of Cork, who 

 possessed some of the types figured in M'Coy's work. This specimen has a pecu- 

 liar imperfection in the front part of the inferior border of the left valve, which 

 is present also in the plaster cast, w T hich removes all doubt of the identity of this 

 specimen being the type. 



This species seems to have had a very limited horizontal distribution, for 

 it has been found only at Little Island, Cork, and even here it seems to be rare, 

 although M'Coy says, "I am assured that they are not uncommon in the Cork 

 limestone." 



De Koninck with strange inconsistency, though apparently always willing 

 to make new species, thought G. ventricosa was only a deformed variety of 

 C. oblonga. Morris and Etheridge also seem to have confounded these two species 



