PLEURONECTITES. 141 



and with its margin confluent with the margin of the body. Margins generally 

 convex, gently concave below the anterior wing. Contour of back gently convex. 



Size. A right valve is 15 mm. long, 16 mm. high, and 3 mm. deep. 



Localities. In the Barnstaple Athenjeum are one left and one right valve from 

 Top Orchard, and left valves from Bradiford, Raleigh, and Kingdon's, Shirwell. 

 In the Porter Collection are three or perhaps four right valves and two left valves 

 from Pilton, and two left valves from Roborough. In my Collection is one doubt- 

 ful right valve from Wrafton Lane. 



Remarks. These specimens are for the most part in a poor state of preserva- 

 tion, and their surface is decayed or gone. They are extremely puzzling from the 

 variety of shapes which they assume, owing probably to the tenuity of the shell. 

 The right valves are, however, easily recognisable by their peculiar convex, 

 radiated, pear-shaped anterior wing. Hence we can identify shells which are 

 inversely oblique with others which are, apparently through squeezing, almost 

 direct. The left valves are sometimes direct, but generally oblique in the opposite 

 direction. It has seemed to me, however, after a careful examination, that this 

 change of shape may be not improbably due to contortion, and therefore I have 

 ventured to place them with these right valves, which otherwise correspond, 

 though I fully realise that the discovery of better preserved specimens may prove 

 them distinct. The figured right valves from Mr. Porter's Collection (PL XVI, 

 figs. 7 and 8) should be regarded as the types of the species ; that in the Barn- 

 staple Museum would have to be separated if further discoveries were to prove 

 that it is not distorted ; while the only left valve that can be certainly referred to 

 it is a very poor specimen of Mr. Porter's, the other left valves being only placed 

 here provisionally until better specimens prove whether they are identical or not. 



Affinities. Pecten consimilis, M'Coy, 1 seems closely related, and has a similarly 

 ornamented ear, but it differs in having its umbo larger and more central, and in 

 being less oblique and very much smaller in size 



Pecten perobliquus , F. A. Romer, 2 seems more oblique and more produced in 

 the postero-inferior part than our right valves, bears no rays on the ear, and 

 has transverse striae on the other parts. 



Crenipecten obsoletus, Hall, 3 and G. glaber, Hall, 4 approach in shape, but neither 

 of them appears to have a radiated ear, and they are probably more equilateral. 



Streblopteria lateralis, de Koninck, 5 comes very close, but does not appear to 

 have a radiated ear, and appears more regularly ovoid in outline. 



Meleagrina Isevigata, M'Coy, 6 seems decidedly more oblique and transverse. 



1 1844, M'Coy, Syn. Garb. Foss. Ireland,' p. 91, pi. xv, fig. 16. 



2 1850, F. A. Eomer, ' Beitr. Harzgeb.,' pt. i, p. 48, pi. viii, fig. 4. 



8 1884, Hall, ' Pal. N. T.,' vol. v, pt. 1, p. 84, pi. ix, figs. 19, 21. 4 Ibid., p. 85, pi. ix, figs. 20, 22 ?. 



5 1885, de Koninck, ' Ann. Mus. Koy. H. N. Belg.,' vol. xi, p. 206, pi. xxxii, fig. 16. 



6 1844, M'Coy, ' Syn. Carb. Foss. Ireland,' p. 80, pi. xii, fig. 5. 



