128 CARBONICOLA, ANTHRACOMYA, AND NAIADITES. 



flat, and is inserted into the shell close to the upper border, whereas it is thick 

 and obovate in Naiadites. 



Many authors have referred specimens of this genus to Myalina, de Koninck ; 

 but this author states in the original description of this genus, "A l'interieur et 

 immediatement au-dessous de ceux-ci (les crochets), une petite lame septiforrne, 

 semblable a celle qu'lon observe dans certaines especes de Mytilus." As I have 

 mentioned above, if Myalina has this septum, Naiadites is at once distinguished 

 by its absence, although Myalina is said to possess a striated hinge-plate. The 

 shells from the Permian of Durham called Myalina squamosa and M. sept/ifera 

 undoubtedly have this septum, and possess the other characters of Myalina 

 enumerated by the author of that name. 



In the ' Geological Magazine,' ]893, vol. x, dec. 3, p. 514, I published a note 

 on the Myalina crassa of Fleming, showing that this shell could not be separated 

 from the genus Anthracoptera (Naiadites) by any one character. M. Barrois 

 (' Recherches sur les terrains anciens des Asturias et de la Galice,' p. 334) 

 remarks on this close resemblance between Myalina, de Koninck, and Anthra- 

 coptera, Salter, and thinks it impossible to distinguish between them; he therefore 

 describes his species as Myalina carinata and M. triangularis, thus making 

 Myalina synonymous with Anthracoptera ; but he did not notice that the lamelli- 

 forin myophore of Myalina was absent in his specimens. De Koninck also says 

 his shell is " equivalve," a character which does not agree with the genus under 

 description. This fact is referred to by M'Coy, 'Brit. Pal. Foss.,' p. 491, note, 

 who quotes and agrees with Professor King, who had stated that the genus 

 Myalina was inequivalve. 



American palaeontologists have always named their Mytiliforni Carboniferous 

 shells Myalina, and indeed prior to his note on these shells in the ' Geol. 

 Surv. Memoir, Geol. Country around Wigan,' 2nd edit., 1862, p. 371, giving the 

 diagnosis of his new genus Anthracoptera, Mr. Salter ('Iron Ores of South 

 Wales,' p. 229) had said, " They have been referred to Avicula, but are probably 

 Myalina;" and he figures the Avicula modiolaris of Sowerb}^ as Anthracomya 

 in pi. ii, fig. 13. 



Mr. Salter's diagnosis of the genus Anthracoptera is as follows : — " They have 

 neither the unequal valves of Avicula nor the striated hinge-plate of Myalina, nor 

 indeed any hinge-plate at all. There is a very obscure tooth in the anterior part 

 of the hinge, but only a, thickened margin to the hinge-line, and no lateral tooth 

 at all," &c. 



This statement I showed to be incorrect (' Quart. Journ. Geol. Soc.,' vol. xlix, 

 p. 250, pi. vii, figs. 1, 1 a, 1 h, 2, 2 a), for there is no doubt as to what shells Mr. 

 Salter referred to, and his Anthracoptera is now known to possess a well-marked 

 striated hinge-plate, unequal valves, and an obscure anterior tooth (PI. XVII, 



