﻿66 



DEVONIAN FAUNA. 



is an aged shell. As the specimen is very imperfect it may appear less convex 

 than it really is. 



Another large specimen in Mr. Vicary's Collection (PI. VII, fig. 2) is interesting 

 from having been broken during life, and mended by a convex patch of shell in 

 which the ribs run obliquely. 



It appears difficult from the state of our material to decide whether 

 A. clathrata, Sandberger, is identical. Its resemblance in shape and in the arrange- 

 ment of the ribs and stride is close, but its ornament seems rather coarser, its 

 shape less convex, its anterior side less steep, and its front wing larger and 

 flatter and less defined. The front wing is, however, very imperfectly seen in all 

 the English specimens. 



I have regarded as belonging to this species a very large and imperfect right 

 valve (PL VIII, fig. 8) in Mr. Vicary's Collection. As it is not in contact with a 

 left valve, and as its ornamentation is very different from that of the other speci- 

 mens, this identification can only be regarded as tentative. But, on the other 

 hand, the close similarity between the mutually corresponding valves of Actin- 

 opteria theta, Hall, and A. ala, Barrande, are strong arguments in its favour, and 

 Mr. Vicary's specimen of the right valve appears to agree more nearly in size 

 and character with the left valves of the present species than with those of any of 

 the adjoining forms. 



Affinities. — Actinopteria theta, Hall, 1 Avicula normata* Barrande, and Avicula 

 (Actinopteria) semiliana, Freeh, 3 are very closely allied species, but all differ 

 in being decidedly broader shells. The transverse ornament on the left valve of 

 A. semiliana is more regular and distant, and the right valve of A. theta has 

 fewer rays. 



Avicula (Pterinea) perdita, Barrande, 4 has every appearance of being simply 

 the right valve of his A. normata, and it is moreover rather broader and smoother 

 than the present fossil. . 



Arinda ala, 5 Barrande, also seems a broader and more quadrate shell. The 

 transverse ridges of its left valve appear to be stronger and more regular, and the 

 hind wing seems shorter. The smoothness of its right valve varies greatly ; the 

 rays on it being sometimes numerous, and sometimes entirely absent except on 

 the wing. 



1 1884, Hall, ' Pal. N. Y.,' vol. v, pt. 1, p. 125, pi. lxxxiv, figs. 18, 19. 



2 1881, Barrande, ' Syat. Sil. Bohem.,' vol. vi, pi. exxv, figs. 4 — 9 ; and pi. ccxxii, figs. 

 17—20, Et. F. 



3 1^91, Freeh, ' Abhandl. Geol. Specialk. Preuss.,' Band ix, pt. 3, p. 43, pi. iii, figs. 1 — 1 b. 

 1 L881, Barrande, ' Syst. Sil. Boliem.,' vol. vi, pi. exxv, figs. 1—3, Et. F. 



6 Ibid., pi. ccv, fig. 3,i—7; pi. ccxvii, fig. 5,1-s; pi. ccxviii, figs. 21—23; and pi. eclxxxi, 

 figs. 1—0, Et. P. 



