﻿62 



DEVONIAN FAUNA. 



Description. — Left valve large, transverse, very oblique, convex. Umbo very 

 anterior. Front wing unseen. Anterior margin rather narrow, receding. 

 Inferior margin very long, oblique, and slightly convex. Postero-inferior corner 

 very much produced, very convex. Posterior margin oblique and nearly straight, 

 becoming erect and concave in the upper part which bounds the hind wing. Hind 

 wing rather small, triangular, flatfish, rather clearly defined, and bearing coarser 

 rays. Contour of surface nearly straight along the line from the deepest point near 

 the umbo to the postero-inferior corner, and nearly evenly convex in the direction 

 perpendicular to this line. Surface covered with multitudinous, minute, distant, 

 elevated, slightly alternating rays, crossed and cancellated by fine, regular, 

 elevated threads, rather more distant than the rays, and by a few coarse bulges 

 or stria; of growth. Hinge-line apparently about two thirds the length of the 

 shell. 



Right valve very similar in shape and convexity to the left, but with its umbo 

 rather less anterior, with a produced front wing, and with a rather broader 

 anterior margin. Hind wing large, undefined. Surface covered by delicate, 

 regular, distant, transverse threads, which are crossed on the postero-superior 

 part, or hind wing, by some rather closer and more rounded, small, irregularly 

 alternating rays. Shell-structure very thin. 



Size. — Length 48 mm., breadth 35 mm., depth of left valve 8 mm. 



Localities. — From Wolborough there is a left valve in the Museum of Practical 

 Geology. From Lummaton there is a left valve in Mr. Lee's Collection in the 

 British Museum, and a right valve and a small and doubtful left valve in my 

 Collection. 



Remarks. — Although many of the most important parts of the shell are very 

 imperfectly indicated by the specimens here described, enough remains to show 

 that they belong to a species distinct from the others which accompany it, though 

 bearing a strong resemblance to some of them. 



The left valve seems distinguished by its short hinge-line, its small hind wing, 

 its fine and numerous ribs, its great length and obliquity, and the delicate regular 

 and distant threads which traverse both the ribs and the furrows. The ribs on 

 the hind wing seem decidedly coarser and larger than those upon other parts of 

 the shell. 



It approaches Avicula (Pterinea ?) ala, Barrande, 1 very closely, but differs by 

 ils much greater length and obliquity, and by its ornament being finer, its 

 postero-inferior corner more produced, and its hind wing apparently smaller and 

 more definite. 



In thai Bohemian shell the two valves are very dissimilar from each other in 



1 1SS1, Barrande, ' Syst. Sil. BoliGme,' vol. vi, pi. ccv, fig. 3, 1—7 ; pi. ccxvii, fig. 5, 1— 3 ; pi. ccxviii, 

 figs. 21 — L>:{ ; and pi. eclxxxi, figs. 1 — 6, Et. F. 



