LEIOPTERIA. 9 



Dimensions.—}']. V, fig. 6, M'Coy's type specimen, measures— 



Antero-posteriorly . . . .36 mm. 



Dorso-ventrally . . . .19 mm. 



From side to side (estimated) . . .4 mm. 



Localities. — England : the Carboniferous Limestone of Grassington, Yorkshire ; 

 Park Hill and Thorpe Cloud, Derbyshire. Ireland : the Carboniferous Limestone 

 of Millicent, Clane, co. Kildare. 



Observations.— Unfovtmiatelj few specimens of this shell have come to my 

 notice. The original of PI. V, fig. 5, is not perfect, and PI. V, fig. 7, a specimen 

 from Grrassington, Yorkshire, in the museum of the Geological Survey, Jermyn 

 Street, is imperfect posteriorly. The species has some resemblance to Aviado- 

 Xtinna viembranacea, de Kon., but the peculiar curvature of the lines of growth 

 j)Osteriorlv is not present in this latter species. 



P. latns is much more regularly triangular and deeper from above downwards 

 than /'. angusfatus. The lines of growth are much less distinctly marked. A 

 single imperfect example has been obtained by me from Thorpe Cloud, and one from 

 Park Hill, Derbyshire. 



Genus Leioi'teuia, Hall, 1884. 



Leiopteria, Hall, 1884. Pal. N. York, vol. v, pt. 1, p. xiii. 

 ? Leptodesma, Hall, 1884. Ibid., p. xiii. 



Generic Gliaracter.t. — Very inequilateral. Shell triangularly oblique, more or 

 less gil)l)ose. Anterior superior angle right. Anterior end short, compressed, 

 marked off from the tumid portion of the valve by the byssal sulcus ; the posterior 

 inferior part of the valve is flattened and rounded ; the posterior margin concave ; 

 the hinge-line straight and more or less prolonged backward beyond the posterior 

 margin as a thin, narrow rostrum. The dorsal slope is flattened, compressed, and 

 expanded into a posterior wing. 



Interior. — The anterior adductor muscle is small, round, deep, placed well within 

 the concavity of the valve, remote from the margin. The posterior adductor 

 larger, shalloAV, placed in the hollow of the dorsal slope, remote from the margin 

 and liinge-line. Pallial line well marked, remote from the margin. Hinge witli 

 oblicpie teeth in front and parallel grooves posteriorl3^ Umbones small, anterior, 

 l)ut never terminal. 



Exterior. — Siu-face marked with lines of growth and striae, at times laminose, at 

 others squamose. Shell thin. 



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