140 CARBONICOLA, ANTHRACOMYA, AND NAITADITES. 
which is the source of hundreds of specimens which I have gathered and studied. 
I have not done this, wishing to avoid confusion and knowing that the names of 
these three forms have been in use for over half a century. 
On looking over the originals of Ludwig’s Dreissenia dilatata and Dreissenia 
Feldmani, | recognised some crushed forms which had I met with in England I 
should have referred to V. carinata, but it is most unsatisfactory to have to speak 
positively on crushed and imperfect specimens, and Ludwig’s figures are utterly 
untrustworthy. At any rate there is no sufficient reason to establish new species 
of a genus which varies so much in shape as Naiadites on poor crushed specimens. 
Mr. Salter’s figure in the ‘Iron Ores of South Wales’ is very good, and evidently 
similar to Sowerby’s type in size and shape; the latter is, however, a little incom- 
plete at the posterior superior angle. When I wrote my paper on the ‘ Affinities 
of Anthracoptera” I had not been able to obtain access to Mr. Etheridge’s 
type specimen of Anthracoptera tumida, and erroneously identified some very tumid 
examples of N. carinata with his species (op. cit., pl. vii, figs. 13,13 a, 14). These 
are to be distinguished by the marked constriction (byssal sinus) anterior to the 
oblique ridge, and by the oblique ridge appearing to more nearly bisect the shell, 
so that the anterior part, though not lobe-like, is large in proportion. 
4, Natapites quaprata (Sowerby). Plate XVIII, figs. 17—21, 23—25. 
Avicuna quaprata, Sow. Trans. Geol. Soc., ser. 2, vol. v, pt. 3, pl. xxxix, fig. 17, 
1836-40. 
— — Brown. Foss. Conch., p. 162, pl. 1xi**, figs. 27, 28, 1849. 
Moptora propucra, Brown. Ibid., p. 1738, pl. lxu, figs. 11, 12. 
Myatia quaprata, Salter. Geol. Surv. Mem. of Gt. Britain, “Iron Ores of 
South Wales,” p. 228, pl. u, fig. 16, 1861. 
? — suBQUADRATA, Shumard. Paleontology Upper Missouri, p. 33. 
? -- MEDINIFORMIS, Meek and Worthen. Paleontology of Illinois, vol. ii; 
Geological Survey of Illinois, 
p- 343, pl. xxvu, fig. 3, 1866. 
ANTHRACOPTERA QUADRATA, Hind. Quart. Journ. Geol. Soc., vol. xlix, p. 254, 
pl. viii, figs. 1—4, 1893. 
Specific Characters.—Shell compressed, produced downwards, quadrate or 
U-shaped, very slightly oblique. The anterior side is almost obsolete, and pointed 
forwards ; the posterior expanded, often to a large extent, and flattened. The 
left valve is somewhat more convex than the right. The anterior margin is almost 
straight, and obliquely cut, there being about its centre, if anything somewhat 
