﻿PTERINOPECTEN. 



81 



low irregularities or bulges. Front wing with only one or two indistinct ribs. 

 Shell-structure papyraceous. Right valve unknown. 



Size. — Length 30 mm., breadth 27 mm., depth of one valve 4 mm. 



Localities. — From Wolborough there is a single fine specimen in Mr. Lee's 

 Collection, another in Mr. Vicary's Collection, and two more in my Collection. 

 From Lummaton there is a specimen in my Collection. 



Remarks. — This is a peculiarly beautiful shell. It is distinguished by its 

 flatness, by its well-defined narrow and almost smooth front ear, by its close 

 rounded ribs, which arise in all parts of the shell, often very near the margins, 

 and by its very regular and close transverse threads or beading. 



Affinities. — Pecten papyraceus, Sowerby, 1 is evidently a proximate form. It 

 is, however, distinguished by its much broader and more convex front wing, by its 

 ornamentation, especially on the wing, and apparently by its greater convexity 

 when it retains its natural shape. 



According to the original figure, Pecten grau.osus, Sowerby, 2 from the Black 

 Limestone of Queen's County, seems to come still closer, and the anterior ear 

 seems similar in shape and in ornament. It is described as " having about thirty 

 granulated very regular rays, and as many nearly smooth ones alternating between 

 them." From this figure and description it might, perhaps, be supposed to be 

 identical, but Irish specimens in the Museum of Practical Geology at once prove 

 it to be quite distinct. Its rays are fewer and coarser, and the cross-strias are 

 very distant and coarsely granulate the ribs. Their front ears also seem to be 

 diverse in character. 



Avicula Neptuni, Goldfuss, 3 has a much broader and differently ornamented 

 front wing. 



Avicula papyracea, Sowerby, sp., as given by Goldfuss,* seems chiefly to differ in 

 having the anterior ear shorter, broader, and strongly rayed, and in being more 

 transverse. 



I formerly thought that my specimen from Wolborough was distinct from the 

 others, and corresponded with Aviculopecten consolans, Barr. 5 Further examina- 

 tion proves this not to be the case. The apparent differences are evidently due 

 to the defectiveness and the crushing of the fossil, while A. consolans, though 

 similar to that shell, is easily distinguishable from the other English specimens. 

 It is a much longer form ; its front wing differs very much in shape, and bears 

 numerous ribs ; its umbo is less central, and its depth is greater. 



1 1822, Sowerby, ' Mm. Conch.,' vol. iv, p. 75, pi. cccliv. 



2 1827, ibid., vol. vi, p. 144, pi. dlxxiv, fig. 2. 



3 1834-40, Goldfuss, ' Petref . Germ.,' vol. ii, p. 125, pi. cxvi, figs. 4 a, b. 



4 Ibid., p. 126, pi. cxvi, figs. 5 a, b. 



5 1881, Barrande, ' Syst. Sil. Bohome,' vol. vi, pi. ccxxii, figs. 2, 1-14, Et. F. 



VOL. II. 



