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DEVONIAN FAUNA. 



Hind wing apparently narrow, flat, ill-defined. Lower margin moderately convex. 

 Contour of surface gently convex on back, steeper in front, and concave near the 

 bind wing. Surface ornamented by between forty and fifty bold, rounded, 

 alternating rays, separated by similar furrows ; about ten of the major series of 

 rays being much larger than the rest, and the rays upon the hind wing becoming 

 smaller, closer, and more equal ; the whole crossed by a series of broad, low, 

 rounded, regular, transverse undulations, in number about twelve. 



Size of left valve. — Length about 35 mm., width 25 mm., depth 7 mm. 



Locality. — A single specimen from Lummaton is in my Collection. 



Remarks. — Unfortunately the hinge-line, wings, and margins of this interesting 

 fossil are so defective and obscured that a complete description is impossible, 

 and an identification difficult. Its shape and ornamentation distinctly separate 

 it from its English comrades. 



There seems no reason to doubt that it belongs to the group of shells of 

 which Aviculopecten consolans, Barrande, Pterinopecten Vertumnus, l&his, and 

 intermedins, Hall, and Aviculojpecten Wnlfi, Freeh, are members. When, however, 

 we proceed to the question of specific identity, the subject becomes more difficult. 

 I am inclined to think after comparing it with the various figures of A. consolans 

 given by Barrande that it falls within the limits of that species. On the other 

 hand, it corresponds minutely in all the points which it actually shows with one 

 of Hall's figures of P. Vertumnus. This American species chiefly differs from the 

 Bohemian shell by having a rather smaller hind wing and more oblique anterior 

 and posterior margins, and in these points the indications in our fossil rather point 

 to the latter, though the small equal ribs of its hind wing agree better with the 

 former. The solution may be that the two foreign shells are really local varieties 

 of the one species, and that the English fossil is a link between them. 



Affinities. — Pterinopecteu Isetus, Hall, 1 has finer and more equal ribs. 



In P. interrurtluis, Hall, 2 the ribs are much smaller and more distant. 



In A. multiplicans, Barrande, 3 the ribs form complex groups. 



In A. Wnlfi, Freeh, 4 the umbo is more central, the shape broader, and the 

 ribs rounder, closer, and more even. 



Pterinopecten gracilinus has finer ribs and is flatter and less transverse in 

 shape than the present specimen. It differs widely from Pt. consolans in 

 other particulars. 



1 1884, Hall, ' Pal. N. Y.,' vol. v, pt. 1, p. 63, pi. i, fig. 13. 



2 Ibid., p. 68, pi. xvii, fig. 19; and pi. lxxxiii, figs. 4, 5. 



• ; lssl, Barrande, ' Syst. Sil. Bohcm.,' vol. vi, pi. ccxxi, figs. 3, i_ 6, Ft. F. 



' 1 891, Freeh, ' Abbandl. Geol. Specialk. Preuss.,' Band ix, pt. 3, p. 26, fig. 1 ; and pi. ii, fig. 7. 



