EDMONDIDiE. 255 



which do not possess a sinuate pallial line and a central cavity in the hinge for 

 the internal cartilage. 



The hinge-apparatus of the genera composing the Edmondidas has been mis- 

 understood, and the small external ligament overlooked. Fischer pointed out 

 that many of de Koninck's species of Edmondia have a very well marked groove 

 for the external ligament, and in consequence erected the genus Pseudedmondia ; 

 but de Koninck states this fact as a generic character, and the latter " genus " is 

 therefore unnecessary. 



De Koninck is evidently at one with me on the close connection between 

 Cardiomorpha and Edmondia, for he says, " II est presque impossible de dis- 

 tinguer les coquilles de ce genre [Edmondia] de celles qui appartientient a 

 certain groupe du genre Cardiomorpha lorsque la charniere fait defaut " (' Ann. 

 Mus. Roy. d'Hist. Nat. Belgique,' vol. xi, p. 28). I am unable to see any real 

 difference in the hinge-plates of the two genera except that due to the peculiar 

 shape and size of the shells. 



I find myself unable to retain the genera Isoculia and Pachydomus which were 

 placed in a group with Cardiomorpha and Edmondia by de Koninck. The former is 

 separated from Cardiomorpha on the supposed presence of a lunule, and its more 

 circular shape and concentric sulcations. The lunule, however, is absent, and I 

 give my reasons at length, under my remarks on Cardiomorpha, for this view. 

 Pachydomus of Morris is stated to have one or two (?) large teeth in each hinge, 

 and deeply excavated muscle-scars, characters which are absent in the shells de 

 Koninck has referred to this genus. 



The genus Scaldia, de Ryckholt, differs from all others in this group in the 

 possession of a single blunt cardinal tooth in each valve, with a corresponding 

 socket, the valves also being orbicular rather than transverse. Externally they 

 closely resemble Edmondia, as de Koninck says, " Les coquilles de ce genre ont 

 le facies des Edmondia et des Cardiomorpha a crochets, non contournes." 



Woodward regarded Scaldia as a sub-genus of Edmondia, and Zittel (' Man. 

 Paleont.,' p. 512) considers the two names synonymous. On examination the 

 fine series of E. Kicksiana in the Museum of Natural History at Brussels shows 

 the tendency of this species to develop the rudiments of a single cardinal tooth, 

 and points to the close connection of Edmondia and Scaldia, the latter species 

 probably being descended from the former, and there is no evidence of au ancestral 

 form with a toothed hinge from which Edmondia could have been evolved. 



The term Cardiomorphidse has been used by Hall (' Pal. New York,' vol. v, 

 pt. 2) and Miller (' North Amer. Greol. and Palseontol.,' p. 458) as a family including 

 Cardiomorpha, Edmondia, Euthydesma, and Protomija, but I am unable to trace 

 the authority for this family. 



Stoliczka, in spite of the non-sinuate pallial line of Edmondia, Cardiomorpha, 



