﻿ACTINOPTERIA. 



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11. Actinopteria ceenatissima, Whidbome, sp. PI. IX, figs. 8, 8 a, 9, 9 a. 



1889. Pteeinea ceenatissima, Whidbome. Geol. Mag., dec. 3, vol. vi, p. 79. 



Description. — Left valve rather large, more or less convex, trapezoidal, not 

 transverse. Umbo large, prominent, incurved, arching forward, and situate 

 at the anterior extremity of the shell. Hinge-margin straight, almost the 

 full length of the shell. Anterior wing unseen, but apparently very small 

 and short. Posterior wing large, undefined, oblique, and triangular. Anterior 

 margin broad, slightly convex and receding. Inferior margin oblique and 

 slightly convex. Postero-inferior corner slightly produced and rounded. 

 Posterior margin slightly oblique and concave. Contour of surface steep 

 in front, sloping more gradually towards the inferior and infero-posterior 

 margins, and slightly concave on the hind wing. Surface covered with nine or 

 ten low, irregular growth-swellings, and with multitudinous, microscopic, close, 

 rounded rays, crossed by still more numerous, crenulated, concentric threads. 



Size of left valve. — Length 41 mm., width 38 mm., depth 9 mm. 



Localities. — There are four specimens in my Collection from Lummaton and 

 one in Mr. Vicary's Collection from Wolborough. 



Remarks. — These shells are distinguished by their broad sub-quadrate shape, 

 and by their exceedingly minute and numerous radiations, which are hardly 

 visible to the naked eye. These rays are slightly undulating, and are crenulated 

 by crowded elevated threads of unequal strength, which are almost foliaceous. 

 There seems to be a considerable amount of variation in the convexity of the 

 specimens. My best shell is decidedly flatter than the rest and has slightly 

 coarser markings, but I do not think that there is any reason to separate it, even 

 as a variety. 



Affinities— Avicula Daleidensis, Steininger, 1 appears to be rather similar in 

 shape, but to have decidedly coarser markings. Steininger describes it as flat. 

 His figure is hardly sufficiently definite for identification. 



Pterinea striatocostata, Giebel, as given by Barrois, 2 is a nearly allied form, 

 and I at one time thought it might be identical. It seems, however, to differ 

 by being a more convex shell, and by having a much broader anterior side, as well 

 as coarser and less granulated ribs. Barrois identifies this shell with Pterinea ? 

 sp., Kayser, 3 which comes even closer to ours, though still differing from it in 

 much the same particulars. Kayser in turn appears to unite his species with 



1 1853, Steininger, ' Geogn. Beschr. Bifel,* p. 56, pi. iv, fig. 7. 



2 1889, Barrois, ' Faun. Calc. d'Erbray,' p. 171, pi. x, figs. 8 a— d. 



3 1878, Kayser, ' Abhandl. Geol. Specialk. Preuss.,' Band ii, pt. 4, p. 135, pi. xix, fig. 4. 



