86 CARBONICOLA, ANTHRACOMYA, AND NAIADITES. 



in Anthraconrya being well developed compared with those in Anodon, and as far 

 as my observations go, are never eroded. The accessory adductor muscle, too, 

 has a different position. I have never been able to make out that Anthracomya 

 possessed a byssus, though, in all species, the valves have a well-marked oblique 

 sulcus and a sinuated inferior border, indicating the connection with a byssiferous 

 ancestor, or that they themselves were byssiferous in the fry. D'Orbigny quotes 

 a byssiferous form of Anodon, being found in the river Parana, South America. 



In my paper on the affinities of this genus in the ' Quarterly Journal of 

 the Geological Society ' (vol. xlix, 1893, p. 258), on similar grounds to those 

 advanced here, I contended for the replacement of this genus in the family 

 Unionidas ; but I was not aware at that time of the extent of the literature of the 

 subject, as may be noted by the number of synonyms given. 



De Ryckholt (' Melanges Paleontologiques,' 1848) appears to have referred 

 some forms of Anthracomya to Cardinia (Agassiz) ; but great uncertainty 

 prevails about de Ryckholt's type-forms, which I am unable to trace ; Professor 

 Dewalque, of Liege, kindly showed me his collection and pointed out forms 

 which he had named after de Ryckholt from the same localities whence the 

 originals were obtained. In looking through the collection in the Brussels 

 Museum I found typical Anthracomya labelled as Cardinia and Mytilus after 

 de Ryckholt. From Mytilus, Anthracomya can easily be distinguished by the 

 absence of the triangular, wedge-shaped form, the non-terminal position of 

 the umbones, the absence of the scars for the byssal muscles, and the erect 

 external ligament. Indeed, Anthracomya aj^proaches far more closely to Modiola, 

 to which genus Brown ('Fossil Conch.,' 1849, p. 172, pi. lxxi, figs. 24, 25; 

 pi. lxxii, figs. 19, 20, 24, 25, 27, 29) and Romer, 1870 (' Geologie und Palaonto- 

 logie von Oberschlesien,' p. 76, foot-note), refer typical shells; but Anthracomya 

 has not the inflated anterior portion, internal ligament, byssus, or muscle-scars of 

 Modiola, and the form and position of the umbones in either genus is markedly 

 different. Anthracomya possesses a well-marked lunule, a character absent in 

 the family Mytilidas. From the sub-genus Modiolopsis, to which shells having 

 the typical appearance of Anthracomya are referred by Eichwald, the same 

 characters will serve as a means of separation. 



Sir W. J. Dawson proposed the name Naiadites for certain Coal-measure 

 Lamellibranchs from Nova Scotia ('Acadian Geology,' p. 43, 1860), but Mr. Salter 

 pointed out that, the group contained members of more than one genus ('Quart. 

 .lomn. Geol. Hoc.,' vol. xix, 1863, p. 80), some of which he correctly referred 

 to his new genus Anthracomya (see also 'Quart. Journ. Geol. Soc.,' 1894, 

 vol. 1, j). 1,37, et seq. ; and antea, pp. 25, 26, and 27). 



Ludwig proposed at, least three names for members of the genus under notice, 

 two of which — Unio and Anodon — need not be more than mentioned here; but it 



