128 CARBONICOLA, ANTHRACOMYA, AND NATADITES. 
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 lintérieur et 
immédiatement au-dessous de ceux-ci (les crochets), une petite lame septiforme, 
semblable 4 celle qu’lon observe dans certaines espéces 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. septifera 
undoubtedly have this septum, and possess the other characters of Myalina 
enumerated by the author of that name. 
In the ‘Geological Magazine, 1893, 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- 
form 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 
by 
Myalina was inequivalve. 
American paleontologists have always named their Mytiliform 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 Sowerby as Anthracomya 
in pl. n, 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, pl. vu, figs. 1, la, 1b, 2, 2a), 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 (Pl. XVI, 
