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DEVONIAN FAUNA. 



a varying number of still finer sub-equal radiations, the whole crossed by 

 numerous, transverse undulations, and by sharp, close growth-strias, which 

 occasionally break the continuity of the ribs. Shell-structure very thin. 



Size of left valve. — About 45 mm. long, 35 mm. broad, and 7 mm. deep. 



Locality. — Wolborough. There is a specimen in Mr. Vicary's Collection. 



Remarks. — This species appears to be well characterised by its ornamentation. 

 The major rays are very small and distant. The number of the minor rays in 

 each interspace varies, there often being four or five in the central parts, and 

 frequently none in the front parts or on the hind wing, while sometimes the central 

 line is larger than the rest. The transverse striae and undulations together result 

 in a rather irregular ornament. The shell is also distinguished from most of the 

 accompanying species, except A.placida, by its greater flatness. I am aware of 

 few, if any, other species which are similarly marked. 



Affinities. — Some specimens of Actinopteria subdecussata, Hall, 1 very nearly 

 approach this shell, but the rays of that species seem to alternate more regularly, 

 and the cross lines to be less crowded. 



4. Actinopteria dilatata, Whidborne, sp. PI. VI, figs. 8 — 10; PI. VII, figs. 1 — 3; 



and PI. VIII, figs. 8, 8 a. 



? 1842. Avicula clathrata, Sandberger. Neues .Tabrb. f. M., p. 397. 

 ? 1848. — — Bronn (pars). Handbucb, pt. 3, p. 1052. 



P1853. — — Sandberger. Verst. Rhein. Nassau, p. 286, pi. xxix, 



figs. 18—18 d. 



1889. Pterinea dilatata, Whidborne. Greol. Mag., dec. 3, vol. vi, p. 79. 

 ? 1891. Avicula clathrata, Freeh. Abbandl. G-eol. Specialk. Preuss., Baud 9, 



pt. 3, p. 41, pi. iii, figs. 10, 10 a. 



Description. — Left valve large, convex, sub-quadrate, transverse. Umbo 

 prominent, wide, rounded, oblique, situated at the anterior end of the hinge-line 

 (excluding the front wing). Hinge-line long, straight, extending almost the 

 extreme length of the shell behind. Front wing apparently small, rounded, 

 convex, and rather undefined. Anterior margin rather narrow, convex, and 

 oblique. Inferior margin very long, slightly oblique, and gently convex. Posterior 

 margin nearly erect and sigmoid. Hind wing long, narrow, sloping, and 

 undefined. Contour of surface convex in the centre, very steep in front, and 

 slightly concave behind the umbo. Surface ornamented with about sixty or 



1 1884, Hall, 'Pal. N. Y.,' vol. v, pt, 1, p. 110, pi. xvii, figs. 23, 24—27, 29—31. 



