EDMONDIA UNIONIFORM1S. 291 



A very large number of species of Edmondia have been described from 

 American Carboniferous rocks, and these are divisible into two groups, the 

 smooth forms and the sulcated. It is difficult to decide, in the absence of 

 material for exact comparison, whether or no any species are common to the 

 Eastern and Western Hemispheres; but with a single exception, E. unioniformis, 

 American authors have come to the conclusion that the species found in the 

 Carboniferous rocks of the West are distinct from those which occur in Europe. 



Waagen does not describe any representatives of the genus Edmondia from 

 the Salt Range of India ; but, as he entirely misconceives the characters of 

 Allorisma, which he figures (' Palasontologica Indica,' sect. 13, pi. xvii, figs. 3, 

 4, and 9) as not possessing an escutcheon, it is not impossible that he may have 

 mistaken species of Edmondia and designated them as belonging to that genus. 



Benshausen figures as Paracyclas proavia, Goldf., sp. (op. supra cit., p. 169), 

 an orbicular shell which has a well-marked, elongate, internal groove in a cast, 

 internal to the umbones, exactly like that which obtains in Edmondia. He says, 

 p. 166, under his generic description, " Ligament von aussen nicht sichtbar, 

 innerlich in einer kiirtzeren oder langeren ausgehohlten Grrube dicht hinter den 

 Wirbeln gelegen." 



This genus possesses hinge-teeth of an orbicular shape, and does not resemble 

 Edmondia in any other character than the possession of the groove for the long 

 narrow process at the back of the hinge-plate, which was evidently not a ligament 

 but a shelly process. The possession in common of such a highly differentiated 

 character, a peculiarity at present known only to be found in these two genera 

 and in Scaldia, seems to me to throw some important light upon the relationship 

 of these two palaeozoic genera. 



Edmondia unioniformis, Phillips, sp., 1836. Plate XXVIII, figs. 1 — 7. 



Isocardia unioniformis, Phillips, 1836. Geo!. Yorks., pt. 2, p. 209, pi. v, fig. 18. 

 Edmondia unioniformis, de Koninck, 1842. Desc. des Anim. loss., p. 67, pi. i, 



figs. 4 a— c. 



— — Morris, 1843. Cat. Brit. Fobs., 1st edit., p. 88. 



— — de Verneuil, 1845. Russia and the Ural Mts., vol. ii, 



p. 299, pi. xix, fig. 18. 

 Keyserling, 1846. Eeise Petschoraland, p. 259. 

 — Bronn, 1848. Nomencl. Pal., p. 452. 



— — Broivn, 1849. Illust. Foss. Concli., p. 198, pi. lxxxi, 



fig. 15. 

 _ _ d'Orbigny, 1850. Prod, de Pal., p. 133, 



Caudiomorpha retrosecta, de Byckholt, 1852. Mel. Pal., 2e partie, p. 100, 



pi. xiii, figs. 15, 16. 

 Pholadomta Vaulxiana, de Byckholt 1852. Ibid., p. 23, pi. xi, figs. 1, 2. 



