NAIADITES TRIANGULARIS. 135 



synonymous. Of this shell be 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 tenua, 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 perfect ; 

 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 

 Hrouutiana 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 ISfaiadites modiolarls 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. 



Naiad ife* modiolarls 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. 



Mytilus triangularis, Sowerby. Trans. Geol. Soc, ser. 2, vol. v, pt. 3, pi. xxxix, 



fig. lb\ 1S40. 



— Toillieziaxis, Je Ryckholt. Melanges Paleontologiques, p. 14 1, pi. viii, 



figs. 13, 1 1, 1852. 



— ampelitj;cola, de Ryckholt. Ibid., p. 143, pi. viii, fig. 17. 

 Mtalina Swallovi, McGhesney. New Sp. Palaeozoic Fossils, p. 57, pi. ii, figs. 6, 6 a, 



1860. 



— — Meek and Wortlien. Greol. of Illinois, Palaeontology, vol. ii, 



p. 341, pi. xxvii, figs. 1 a — J, 1866. 



