﻿LEIOPTERIA. 



79 



projecting above the hinge-line, and situated probably at about its anterior third. 

 Hinge-line straight, thickened, more than half the total length of the shell. Wino- 3 

 small, narrow, seemingly concave. Posterior wing apparently about twice the 

 size of the front wing. Anterior margin, below the wing, narrow and very convex. 

 Inferior margin oblique and slightly convex. Infero-posterior margin very broad 

 and regularly convex. Supero-posterior margin straight and very oblique, till it 

 becomes sharply concave on the wing. Contour of surface gently rounded on the 

 back, sinking steeply to the front, and sloping out more flatly to the rear. 

 Surface bearing several irregularly arranged and slightly foliaceous growth-lines 

 so as to present a tendency to alternating sharpish ridges and depressions. Shell- 

 structure papyraceous. 



Size. — Length 20 mm., width 16 mm., depth 4 mm. 



Locality. — There is a single specimen from Xewton (Wolborough ? in the Lee 

 Collection in the British Museum. 



Remarks. — This is a peculiarly neat and graceful shell, and is very different 

 from any of the accompanying species. It is distinguished by its obliquely ovoid 

 form, by the absence of radiating stria?, and by its concentric markings, which 

 are more in the nature of changes of surface level than of defined ornament. 

 Both wings are defective in the specimen, the hinge-line being injured at both 

 extremities, and the front wing obscured by matrix. Their general form can, 

 however, be pretty clearly traced. There are a few indistinct, radiating 

 markings on the back, which may, perhaps, be the remains of colour-lines, as 

 they do not seem to affect the level of the surface. 



Affinities. — It seems to be somewhat similar to a fossil described by Holzapfel 

 as Pterinea, n. sp., 1 which differs in being much smaller, longer, and more coarsely 

 ornamented, and in not showing any defined wings. As, however, Holzapfel's 

 figure is very small, it is possible that these differences may be accidents of the 

 drawing, but, if they are correct, his shell ought, I think, rather to be referred 

 to the genus Posidonomya. 



Avicula incisa, Barrande, 2 differs in having a longer hinge-line, a more curved 

 inferior margin, and a shorter anterior side. 



CUnopistha lata, de Koninck, 3 is at first sight strikingly like, but a closer 

 comparison at once shows that this likeness is purely superficial, and that its 

 generic characteristics are totally different. 



The various species of L> iopteria, Hall, described by himself and de KoDinck,* 

 all differ in having the anterior side much narrower and more oblique, but in other 



1 1882, Holzapfel, ' Palseontographica,' vol. xxviii, p. 258, pi. xlix, fig. 12. 



- 1881, Barrande, ' Syst. Sil. BohSme,' vol. vi. pt. 1, pi. exx, figs. 1—3, fit. D. 



3 1885. do Koninck, ' Ann. Mus. Hoy. H. N. Belg.,' vol. ix, pt. 5, p. 124, pi. xii, figs. 5, 6. 



* 1 bid.. p. 187, pi. xxx. 



