258 CARBONIFEROUS LAMELLIBRANCHIATA. 



oblique ridges, e. g. Cardiomorpha alata and C. Humbolti, and I question the 

 advisability of expanding the genus in order to receive them. I have never been 

 able to observe a lunule in the typical species of Cardlomorpha, and, as defined by 

 de Koninck, this genus does not contain transverse shells with an ornament 

 consisting of concentric sulci. 



The figures of Edmondia gigas from the upper part of the Middle Devonian of 

 West Germany given by Beushausen (op. cit.) seem to me to be characteristic of 

 the genus Cardiomorpha rather than that to which it is referred, and much more 

 in accordance with it than any of those shells placed in the genus by that 

 author. 



De Koninck described eighteen species, seventeen of which were said to be 

 new ; many of them are probably synonymous, and due to slight variations in 

 shape, and to the fact that several specimens are in different stages of growth. 

 The distribution of these species is as follows : 



Etage III. — Visean . . . . .5 



,, II. — Waulsortian . . . .12 



„ I. — Tournaisian . . . .1 



18 



— the idea being that each species is confined to its own horizon. Curiously 

 enough, the common forms, C. communis and C. oblonga, which are said to be 

 confined to etage II in Belgium, are in Great Britain found in the limestones 

 characterised by the presence of Productus giganteus, which is considered as 

 typical of etage I, the Visean in Belgium. Fifteen out of the eighteen species are 

 stated to be more or less rare. The description of fourteen species is from the 

 pen of Prof. Jules Fraipont. 



I am able to recognise only at most half a dozen of the species, as many of 

 the shells described as new species are simply different stages of growth of the 

 common forms, or differ merely in some slight details of comparative measure- 

 ment. Although in the possession of markedly prosogyrous umbones, Cardio- 

 morpha has a close resemblance to Isocardia ; its edentulous hinge-plate at once 

 separates the two genera. 



De Koninck separated the Cardiomorpha corrugata, M'Coy, from Cardiomorpha 

 on the ground that the former possessed a lunule, concentric folds, and umbones 

 less enrolled. I cannot agree with him on these points ; and, as I point out under 

 my observations on G. corrugata, the species has no more trace of a lunule than 

 any of the other species of the genus. I would also add that, few though they 

 be, C. ventricosa possesses well-marked concentric grooves. The hinge-characters, 

 judging from casts and internal anatomy, are identical in G. corrugata and the 

 other species, and I can see no real grounds for retaining the genus Isoculia. 



