fine close concentric striæ, or else toothed, especially on the only remaining ear.
Loc. and Horizon. In shale, with other marine fossils, at Woodhall Mill, as before.
Genus Anthracoptera, Salter.
Anthracoptera, Salter, 1862, Mem. Geol. Survey, Country around Wigan, p. 37.
Gen. char. Shell aviculiform, very slightly inequivalve, with a slight byssal notch in both valves; left valve the most convex. Hinge-line with a thickened margin, but no hinge-plate of any kind; there is an obscure tooth in the anterior part of the hinge, but no lateral teeth. Posterior adductor scar large and subcentral; anterior scar small, umbonal, with at least two supplementary scars; shell thin, with a puckered or plaited epidermis. (Salter.)
Obs. The genus Anthracoptera was proposed by the late Mr. Salter to include numerous Coal-measure shells " hitherto called Myalina or Avicula with doubt, but evidently distinct from one and the other of these genera. They have not the unequal valves of Avicula nor the striated hinge-plate of Myalina, nor indeed any hinge-plate at all." I now propose to place in this genus, in addition to the Coal-measure fossils for which it was established, some bivalves from the Lower Carboniferous rocks of this neighbourhood, of which the internal characters of the shell, so far as I have been able to make them out, appear to have more in common with this genus than with Myalina. About two or three years before Mr. Salter proposed his name, Dr. Dawson established his genus Naiadites for similar shells, characteristic of the South-Joggins Coal-measures, Nova Scotia. In a paper on "Fossil Shells from the Coal-measures of Nova Scotia"[1], Mr. Salter pointed out the synonymy of the two names, and claimed for his own precedence over that of Dr. Dawson on the ground of more complete description. Anthracoptera appears to have been regarded by Salter as one of either the Aviculidæ or Mytilidæ, whilst by Dr. Geinitz the typical American species, A. (Naiadites) carbonaria, Dawson, is looked upon as a Dreissena[2]. The affinity of these shells has been discussed by Dr. Dawson at some length; he considers them to be brackish-water shells allied to the Mytilidæ, or embryonic forms of Unionidæ[3], and states that the structure of the shell is similar to that of the latter family.
Anthracoptera? obesa, sp. nov. Pl. I. figs. 12, 13 (& 14?).
Sp. char. Trigonal, very gibbous, inequality of the valves distinctly marked; anterior side pointed, well marked, and defined by the byssal furrow in each valve; posterior side but little flattened, its
