﻿8G 



DEVONIAN FAUNA. 



immediately below the wing, and much produced and rapidly convex in the lower 

 part. Contour of surface slightly convex in the central region, and flattening out 

 to the margin. Surface marked by about sixty low, fine, very distant, sharpish, 

 alternating ribs, separated by broad, flat interspaces, of which a few are generally 

 visible on the umbo, but most start at different points lower down on the back of 

 the shell ; the whole crossed by occasional, low, concentric bulges or inequalities, 

 and by very indistinct, close, fine, concentric striae. Wings similarly, but more 

 finely, marked. Shell-structure papyraceous. Left valve unknown. 



Size. — Length 26 mm., breadth 23 mm., depth of left valve about 3 mm. 



Localities. — From Wolborough there are three specimens in Mr. Vicary's 

 Collection, and three in the Museum of Practical Geology. From Lummaton 

 there are two specimens in my Collection ; three specimens in the Torquay 

 Museum probably came from the same locality or from Barton. 



Remarks. — While presenting the same general characters, the specimens above 

 enumerated show considerable variation in detail, and, unfortunately, they are not 

 sufficiently perfect to be easily compared. Thus they seem to vary considerably 

 in length and obliquity, in the smoothness of the shell about the umbo, and in the 

 distinctness of the transverse striae. I have, however, been unable to find 

 anything like specific differences in them, and in this view I had the support of 

 my friend the late Mr. Tom Roberts when we examined them together. The 

 species must therefore be regarded as somewhat variable. 



Affinities. — I have met with no described shell hitherto with which they could 

 be classed. 



3. Genus. — Lyriopecten, Hall, 1883. 



This genus or sub-genus contains Aviculopectens, which have short hinge-lines 

 and small ears, and which are sub-circular in shape. 



Freeh has substituted the name Orbipecten because Hall had originally used for 

 them the name Lijropecten, which had been preoccupied by Conrad for a different 

 genus of more recent shells. As, however, Hall has himself changed his name to 

 Lyriopecten there seems no logical reason for any further alteration. 



The group or genus appears to have been confined to the Devonian period. 



1. Lyriopecten fibratus, n. sp. PI. VI, figs. 1, 1 a, 1 b. 



Description. — Left valve large, flat, wider than long, equilateral, sub-circular. 

 Umbo minute, direct, sharp, low, proximate, not elevated above the hinge-line, 

 and situated slightly in front of its central point. Hinge-line straight, long, 

 probably about two-thirds the length of the shell. Front wing rather large, 



