NAIADITES. 129 



figs. 8 — 10, 12 — 15); but at that time I kept Mr. Salter's name. On the pub- 

 lication of this paper Sir W. J. Dawson wrote to me that he considered his name 

 Naiadites, published in the Supplementary Chapter, 'Acadian Geology,' 1860, p. 43, 

 bad prior claim to Mr. Salter's Anthracoptera, and tbat he had had some corres- 

 pondence with him on the subject ; so much so that when Salter was describing some 

 remains from the South Joggins Coal-field, 'Quart. Journ. Geol. Soc.,' vol. xix, p. 80, 

 1863, he figured some specimens which W. J. Dawson had sent him as Anthracomya 

 (Naiadites) and Anthracoptera (Naiadites). In the next edition of the 'Acadian 

 Geology,' 1868, p. 204, we find W. J. Dawson refers his shells to Naiadites 

 (Anthracomya), and Naiadites (Anthracoptera). 



Under the term Naiadites were described and figured seven shells, the first 

 only really belonging to Mr. Salter's genus, the majority belonging to Anthracomya, 

 and one only to Carbonicola. Under these circumstances Sir W. J. Dawson and I 

 agreed to substitute his name of Naiadites for Mr. Salter's Anthracomya, and we 

 placed before the Geological Society a joint note to this effect ; but it was pointed 

 out that the name should lie retained for the first shell in the list rather than for 

 the majority. This shell happened to be Naiadites carbonaria, and consequently I 

 altered my note to suit this view, and replaced Mr. Salter's genus of Anthracoptera 

 of 1862 by Sir W. J. Dawson's Naiadites of 1860. The question then arose as to 

 whether de Koninck's Myalina might not even supersede Naiadites, as from my 

 discovery of the striated hinge-plate, the great point on which Mr. Salter relied for 

 separate diagnosis was removed ; but there still remained the fact that de Koninck 

 affirmed a rostral plate or myophore in his description, which was, however, con- 

 spicuously absent in his figures, and more markedly so in the illustrations in pi. xxix 

 of his later work, ' Faune du Calcaire carbonifere de la Belgique,' 1885. In the text 

 he states, p. 168, " J. W. Salter a cree en 1863 pour quelques especes mytiliformes 

 provenant des assises inferieures de terrain houillier, le genre Anthracoptera; 

 celui-ci a aussi beaucoup d'analogie avec le genre Myalina, mais sa charniere est 

 eofalment mince et lineaire et son lio-ament est externe." This is rather a, curious 

 remark, as a few lines above he had stated, " Bord cardinal epais, plat, avec 

 plusieurs rainures longitudinales de cartilage." 



It is quite possible that all de Koninck's species of Myalina differ from those of 

 Naiadites, as the former are all stated to be from the Calcaire carbonifere of Vise, 

 where they are associated with a typical marine fauna. M'Coy (' British Paleozoic 

 Fossils,' p. 402) says in his description of Myalina there is "a triangular septum 

 in the cavity of each beak, parallel with the plane of the lateral margins (leaving 

 deep- slits under the beaks of the casts)," but he makes no mention of specimens of 

 this genus from British Carboniferous rocks. I have therefore adopted the name 

 Naiadites (Dawson) for the Mytiliform shells of the Coal-measures for a twofold 

 reason. First, because thev do not possess myophorial septa; and second, 



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