﻿ACTINOPTERIA. 



67 



Pterinea lineata, Goldfuss 1 (which includes Pt. plana, Goldfuss, 2 and Pt. 

 elongata, Goldfuss, 3 according to Freeh*), appears distinguished by a much more 

 defined and usually much longer hind wing, and by finer radiations. 



Avicula intermedia , ffihlert, 5 seems more triangular in shape, being much more 

 truncated in the anteroinferior region. 



Avicula cancellata, Phillips, 6 from North Devon, might, as figured by him, 

 perhaps be supposed to be identical. Specimens, however, in Mr. Hall's collection 

 and in the Museum of Practical Geology, which evidently belong to that species, 

 show that it is a shell of a different type. Its general contour is different and its 

 ribs are finer and not alternating. It belongs, with its cogener Avicula Dam- 

 noniensis, Sowerby, 7 to the group of shells which Hall has separated under the 

 generic name of Ptychopteria* 



5. Actinopteria placida, Whidbome, sp. PI. VII, figs. 5 — 11 ; and PI. VIII, 



figs. 7, 7 a. 



1887. Actinopteria Botdi, Tschemyschew (not Conrad). Mem. Com. Geol. 



Russ., vol. iii, pt. 3, p. 44, pi. vi, 

 figs. 18—20. 



1889. Pterinea placida, Whidbome. Geol. Mag., dec. 3, vol. vi, p. 79. 

 1889. — obovata, Whidbome. Ibid., dec. 3, vol. vi, p. 79. 



Description. — Left valve small, sub-quadrate, oblique, rather transverse, 

 moderately convex. Umbo prominent, oblique, incurved, proximate, extending 

 slightly above the hinge-line, and situated at the anterior quarter of its length 

 (including the anterior wing). Anterior wing very large, broad, convex, trape- 

 zoidal, defined by a shallow concavity from the umbo, and ornamented by about 

 ten coarse, close rays. Posterior wing large, flattish, triangular, slightly defined, 

 and bearing about twelve coarse, rounded, and rather close rays. Anterior 

 margin oblique, slightly notched under the wing, and convex below it. Inferior 

 margin wide, slightly oblique, and convex. Postero-inferior corner broadly 

 rounded. Posterior margin nearly erect and slightly concave. Hinge-line 

 straight and equal to the greatest length of the shell. Contour of surface 

 gently convex, sinking suddenly to the anterior wing and rather more gradually 



1 1834-40, Goldfuss, ' Petref. Germ.,' vol. ii, p. 135, pi. cxix, figs. G a— c. 



2 Ibid., p. 135, pi. cxix, figs. 4 a— -f. 



3 Ibid., p. 135, pi. cxix, figs. 5 a — c. 



4 1891, Frecb, ' Abhandl. Geol. Specialk. Preuss.,' Band ix, pt. 3, p. 89, pi. ix, figs. 17—19. 



5 1881, OShlert, ' Mem. Soc. Geol. Fr.,' ser. 3, vol. ii, p- 21, pi. iii, figs. 1— 1 c. 



6 1841, Phillips, 'Pal. Foss.,' p. 49, pi. xxii, fig. 84. 



7 1840, Sowerby, ' Geol. Trans.,' ser. 2, vol. v, pt. 3, pi. liii, fig. 22. 



8 1884, Hall, ' Pal. N. Y.,' vol. v, pt. 1, p. xii. 



