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DEVONIAN FAUNA. 



1. ACTINOPTERIA ? ROBERTSII, n. Sp. PI. VI, figS. 2 4. 



Description. — Left valve small, oblique, convex, transverse. Umbo small, 

 anterior, proximate. Anterior wing small, obtuse, convex, divided from the back 

 by a sharp concave depression. Posterior wing small, triangular, flat, sharply 

 defined. Hinge-line rather short, being less than half the length of the shell. 

 Anterior margin convex above, straight and oblique below. Inferior margin oblique 

 and gently convex. Postero-inferior corner much produced and very convex. 

 Posterior margin oblique and straight below, becoming broadly concave above, 

 where it bounds the wing. Contour of surface convex, the highest line running 

 down from the umbo to the postero-inferior corner, and the surface sloping from 

 it more steeply on the posterior than the anterior side. Surface of wings almost 

 smooth, or marked by sharp, distant growth-ridges. Surface of back bearing 

 between twenty-five and thirty very distant, small, sharp rays, divided by broad 

 and slightly concave interspaces, and crossed by sharp, distant, irregular, and 

 indistinct threads or growth-lines. 



Size. — Length 20 mm., breadth 16 mm., depth of left valve 4 mm. 



Locality. — Lummaton. There are seven specimens in my Collection, and two 

 in the Woodwardian Museum. 



Remarks. — This species is distinguished by the shape of its wings ; the front 

 wing being short, swollen, and rounded, and the hind wing being very small, flat, 

 triangular, well-defined, and with a concave posterior margin. Its ornament is 

 also characteristic, the ribs being few in number, narrow and sharp, and much 

 more prominent than the distant, transverse strige or threads on the body of the 

 shell, while on the wings the latter become stronger, and the former almost 

 entirely disappear. It would seem, however, that on the hind wing at least six or 

 seven rays were normally present, but these are generally obliterated either 

 during life or fossilization. 



Affinities. — I have met with few foreign species that approach it closely except 

 Avicula immunis, Barrande. 



Beushauseu's 1 figure of A. Jugleri, F. A. Romer, 2 agrees in the shape of its 

 hind wing, but its anterior side is different, and its ribs are stronger and closer. 

 As given by F. A. Romer and Freeh 3 this species is widely distinct. 



Arte itla mucro, Barrande, 4 has a much smaller front wing, and differs in the 



1 1884, Beushausen, ' Abhandl. Geo]. Specialk. Preuss.,' Baud vi, pt. 1, p. 55, pi. ii, fig. 9. 



2 1 8 13, F. A. Bonier, ' Verst. Harzgeb.,' p. 21, pi. vi, fig. 4. 



3 1S91, Freeh, ' Abhandl. Geol. Specialk. Preuss.,' Band ix, pt. 3, p. 18, pi. xvii, fig. 2. 

 1 1881, Barrande, ' Syst. Sil. Bohem.,' vol. vi, pi. ccxviii, figs. 7 — 10, Et. E. 



