E. ETHERIDOE, JUN., ON LOWER- CARBONIFEROUS INVERTEBRATA. 13 



margin slightly sigmoidal. Hinge-line straight, as long as the 

 shell, its margin thickened on each valve, leaving in casts two long 

 grooves. Umbones well developed, contiguous, but not touching, 

 anterior, but not quite terminal, with a broad, very obtusely rounded 

 diagonal ridge proceeding from each, to which the shell owes much 

 of its exceedingly convex form. Byssal furrows shallow, most pro- 

 nounced in the left valve ; marginal notch not deeply excavated. 

 Anterior muscular impressions quite anterior, infra-umbonal. Sur- 

 face of the shell covered with concentric subimbricating lamellae, 

 crowded and striiform on the anterior end, but opening out and 

 becoming lamellar on the diagonal ridge and posterior wing. 



Obs. The shells comprised in this species very much resemble 

 some Myalina? ; but I believe I am more justified in referring them 

 to the present genus than to Myalina, of the striated hinge-plate 

 of which I can find no trace ; neither has any definite evidence pre- 

 sented itself which would warrant me in placing them in either 

 Avicula or Pterinea. The much more central position of the dia- 

 gonal ridge, greater convexity of the shell, and the sigmoidal margin 

 of the posterior end at once distinguish A. obesa from either 

 Anthracoptera? or Myalina (Avicula) quad?' ata, Sow., A.? or M. 

 (Avicula) modiolaris, Sow., A. ? or M. (Modiola) carinata, Sow. *, 

 or Anthracoptera? Browniana, Salter (= Avicula tenua, Brown). 

 I am not acquainted, and so cannot institute a comparison, with 

 any of those Coal-measure fossils figured by Captain T. Brown in 

 his ' Fossil Conchology ' f , many of which will doubtless fall into 

 the genus Anthracoptera ; but A. obesa appears to be quite distinct. 



Loc. and Horizon. In a bed of hard micaceous sandstone, Drums- 

 heugh, Water of Leith, at Dean Bridge, Edinburgh, Wardie-Shale 

 division of the Cement-stone group; in altered shale underlying 

 trap, Corstorphine Hill, near Edinburgh ; in a band of limestone 

 above the sandstone at Craigleith Quarry, near Edinburgh? 



Genus Myalina, De Koninck. 

 Myalina, De Koninck, Anim. Eoss. Terr. Carb. Belgique, p. 125. 



Myalina crassa, Eleming (non Gr. & E. Sandberger). 



Yar. modioliformis, Brown. 



Obs. In the ' Annals and Magazine of Natural History ' for June 

 1875 I described a series of specimens of M. crassa, Elem., from the 

 Fife Carboniferous-Limestone series and the Lower Carboniferous 

 of this neighbourhood, and gave the synonymy of the species as 

 then known to me. I remarked on the slighter make of the latter 

 as compared with the Eife examples. I find that the Water-of- 

 Leith shells from the Lower Carboniferous rocks were described 



* In one place Mr. Salter referred these species to Myalina (Iron Ores Gt. 

 Britain, 1861, pt. 3, p. 228), in another with doubt to Anthracomya (ibid. 

 p. 230), and again in a third to Anthracoptera (Oldham Memoir, 1864, p. 64). 

 He appears to have been in great doubt as to their true generic affinity. 



t Plate 62. 



