CARDIOMORPHA OBLONGA. 261 



examined, but it was probably lodged in a narrow groove above the binge-plate, 

 which is seen between the umbones. 



Exterior. — The surface of the shell is covered in front with numerous very fine 

 strige and lines of growth, arranged concentrically ; but over the greater portion 

 of the shell posteriorly the surface is smooth. Shell very thin. 



Dimensions. — Fig. 2, PI. XXI, the largest example I have met with, measures — 

 Antero-posteriorly . . . .76 mm. 



Dorso-ventrally . . . .58 mm. 



From side to side . . . .47 mm. 



Localities. — England : the Carboniferous Limestone of Thorpe Cloud and 

 Castleton, Derbyshire ; Clifton, near Bristol. The Isle of Man. Scotland: the 

 Lower Limestone series of Gameshill, Stewarton. Ireland : the Carboniferous 

 Limestone of St. Dooghlas and Blackrock, near Dublin ; Millicent, co. Cork ; 

 Kildare ; Rathkeale and Limerick. 



Observations. — The original type of Sowerby's Isocardia oblong a appears to have 

 been lost, but that of Phillips is in the Gilbertson Collection of the British 

 Museum (Nat. Hist.), South Kensington, and I am able to reproduce it by 

 the kindness of the authorities. Sowerby's specimen is stated to have been 

 obtained from Blackrock, co. Dublin ; and I am able to figure a fine specimen 

 from this locality, from the collection of Mr. Joseph Wright of Belfast, 

 PL XXI, fig. 1. De Koniuck thought that the specimen figured by Phillips, 

 PI. XXI, fig. 5, did not belong to the same species as that of Sowerby, and 

 gave it a new name, C. Woodwardi. The distinctive character of this species 

 is that the dorso-ventral diameter is equal to the transverse ; or, judging from 

 the figures in the ' Descript. des Anim. foss.,' pi. ii, figs. 7a,b,c, apparently 

 even greater. Woodward pointed out that de Koninck's specimen was wrongly 

 referred to Sowerby's species (' Manual Mollusca,' p. 323) ; but I think de 

 Koninek was in error in placing Phillips's shell in the same species, and consider 

 that the original determination was the correct one. 



In de Koninck's last work Fraipont has described a number of species of 

 Cardiomorpha, which I can but regard as synonymous with G. oblonga. The 

 examination of a fair number of specimens from British localities shows that this 

 species varies somewhat in the comparative dimensions in almost each individual 

 case, and it is easy to find in a series from one locality specimens which possess the 

 characters given by Fraipont as distinctive of the numerous species he describes. 

 The characters are, without exception, mere differences in comparative measure- 

 ment, which cannot be accepted, as possessing specific value. I therefore regard 

 C. quadrata, G. Etheridgei, C. elegans, and G. lata as synonyms of G. oblonga; 

 and possibly C. ovata should be added to these. 



