140 CARBONICOLA, ANTHRACOMYA, AND NAIADITES. 



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, 1 recognised some crushed forms which had I met with in England I 

 should have referred to N. 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 2V. carinata with his species (op. cit., pi. 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. Naiadites quadrata (Sowerby). Plate XVIII, figs. 17—21, 23—25. 



Avicula quadrata, Soiv. Trans. Geol. Soc, ser. 2, vol v, pt. 3, pi. xxxix, fig. 17, 



1836-40. 

 _ _ Broion. Foss. Conch., p. 162, pi. lxi**, figs. 27, 28, 1849. 



Modiola producta, Brown. Ibid., p. 173, pi. Ixii, figs. 11, 12. 

 Myalina quadrata, Salter. Geol. Surv. Mem. of Gt. Britain, " Iron Ores of 



South Wales," p. 228, pi. ii, fig. 16, 1801. 

 ? subquadeata, Shumard. Palaeontology Upper Missouri, p. 33. 



melinieormis, Meek and Worthen. Palaeontology of Illinois, vol. ii ; 



Geological Survey of Illinois, 

 p. 343, pi. xxvii, fig. 3, 1866. 

 Anthracoptera quadrata, Hind. Quart. Jouru. Geol. Soc, vol. xlix, p. 254, 



pi. 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 



