NAIADITES TRIANGULARIS. 135 
synonymous. Of this shell he gives the following description :—“It is 
exceedingly thin, almost papery in texture, and so little can be seen of the 
hinge or muscular impressions that I do not feel sure it belongs to the 
genus here for the first time proposed.” This speaks for itself, and a comparison 
of Captain Brown’s with Mr. Salter’s half-real, half-ideal figures will render 
the species Anthracoptera Browniana of Salter exceedingly problematical. There 
exists, as far as I can see, no excuse for the change of Captain Brown’s 
specific name of tenwa, which had not been appropriated in Mr. Salter’s new 
genus. I suspect that Captain Brown’s shell will probably turn out to be 
Posidonia, which is very abundant in some beds of the Lancashire Coal-field. I 
would point out, too, that Captain Brown represented his specimens as_pertect ; 
but Mr. Salter, to transform the shell into his new genus, dotted in a hypo- 
thetical outline. In most museums and collections the name Anthracoptera 
Browniana was given to such flattened and crushed specimens as were too 
imperfect to identify with other forms. I have therefore seen no reason for 
retaining a name, in respect of which even the author himself seems to have had 
considerable doubt. 
Mr. John Ward’s determination of Naiadites modiolaris as Anthracomya modio- 
laris is evidently due to Mr. Salter’s misleading statement quoted above, for the 
figure in the ‘ Iron-ores of South Wales’ is referred to in support of his opinion. 
Naiadites modiolaris is somewhat variable in shape, but always is more nearly 
a right-angled triangle than any of the other species of this genus. The hinge- 
line may be as long as, longer than, or even less than the greatest length of the 
shell; this may be due, as I have pointed out above, to the accidental non- 
preservation of this posterior edge of the shell; the variation also from the angle 
made by the junction of the posterior and superior borders to a blunt curve is 
probably due to the same cause, i.e. casts of the interior do not show the 
extreme length or accurate shape of the posterior end, for here the two valves 
came absolutely into contact. 
2. NAIADITES TRIANGULARIS, Sowerby. Plate XVII, figs. 31—38. 
Myrinus TrIancuLanrts, Sowerby. Trans. Geol. Soc., ser. 2, vol. v, pt. 3, pl. xxxix, 
fig. 16, 1840. 
— TornLinzianus, de Ryckholt. Mélanges Paléontologiques, p. 141, pl. viii, 
figs. 13, 14, 1852. 
— AMPELITEHCOLA, de Ryckholt. Ibid., p. 143, pl. viii, fig. 17. 
Myatina Swaxt.ovi, UcChesney. New Sp. Paleozoic Fossils, p. 57, pl. 11, figs. 6, 6 a, 
1860. 
_ — Meek and Worthen. Geol. of Illinois, Paleontology, vol. ii, 
p. 341, pl. xxvii, figs. 1 a—d, 1866. 
