134 CARBONICOLA, ANTHRACOMYA, AND NAIAD1TES. 



the Coal Shale of Moris should be referred to the species under discussion. His 

 description is " Coquille un pen triangular, anguleuse, tres-in equilateral, retrecie et 

 emousee enarriere, dilateeet arondie en avant ; .... cote cardinal droit ; region du 

 ligament comprimee ; region palleale renflee," which corresponds very well with 

 that given above. Isaac Lea gives a typical figure of Naiad ites modiolaris under 

 the name Modiola Wyoming ensis (op. supra cit.) from the Coal-measures in the 

 neighbourhood of Wilkesbarre. His description is " Testa lasvi triangulari 

 inferne compresso-alata ; umbonibus elevatis acute angulatis ;" and he remarks, 

 " This is a broad, flat species." Scales of Palasoniscus occurred with the shells. 



Ludwig appears to have divided this species into three, to each of which he 



gave names, apparently unaware that Sowerby and Brown had already done the 



same thing between them, and to an equal extent. I have had the good fortune 



in this case to see the original specimens now in the Museum at Dresden, and 



find that the fossils so beautifully drawn are embedded to a large extent in the 



matrix and are very imperfect. I was unable to see on what grounds Dreisseida 



hiriuiosa was divided from Dreixsenia dilatata. The former is said to be sharply 



triangular "am unteren Ende dreizipfelige," while D. dilatata is " unten stumpf 



zugerundete ;" but in many cases the shells are so compressed and distorted as to 



render it unsafe to erect species upon them. Fig. 10, pi. xxi, op. cit., the 



drawing of D. inflata,is a pure invention, the specimen being not a fossil at all, but 



a clay-ironstone concretion. It is noteworthy of Mr. Salter's great uncertainty of 



the real affinities of some of the Coal-measure shells that in the Geological Survey 



Memoir ' The Iron Ores of South Wales,' on p. 228, he gave " Myalina modiolaris 



{Avicula, ' G. Tr.,' pi. xxxix, fig. 18), pi. ii, fig. 14," and on p. 230, "A. ?sp. 



(Avicula modiolaris, Sow.), pi. ii, fig. 14, aberrant form;" thus referring the figure 



of one shell to two different genera. The " diagram of the general shape and 



characters" of Anthracoptera, given with his original description by Mr. Salter, 



1 Memoirs Geological Survey, Great Britain,' "Geology of the Country around 



Wigan," 2nd edit., Appendix, p. 38, 1862, might have been drawn from a typical 



specimen of N. modiolaris; it possesses the emarginate posterior border which 



would become trifid if the shell were flattened, and would appear like Ludwig's 



Dreissenia laciniosa. This condition is very rare, being naturally absent in casts, 



and, owing to I lie extreme fragility of the shell at the posterior border, is rarely 



preserved except in specimens crushed fiat in the shale. The presence or absence, 



then, of this emarginate posterior border is not of specific value, being present or 



absenl according to the state of preservation of the fossil. In the same volume 



and on the same page from which I have just quoted Mr. Salter describes 



a new shell as Anthracoptera ? Browniana, with which he states Avicula tenua, 



referred to by Mi'. Binney in the ' Manchester Geol. Trans.,' vol. i, p. 161, pi. v, 



fig. 23, and described by Brown in ' Foss. Conch.,' p. 161, pi. lxviii, fig. 9, is 



