PANENKA. 73 



which the eight or ten situated medianly are decidedly narrower than those on 

 each side, and which seem gradually to increase in size laterally, and are divided 

 by concave furrows narrower than the ribs. Transverse ornament consisting of 

 numerous regular, fine, close, strong, transverse striae or threads, which cross the 

 ribs as well as their intervals. 



Size of a distorted specimen : height 60 mm., length 70 mm., depth 15 mm. 



Localities. — An imperfect and distorted specimen from Top Orchard is in the 

 Barnstaple Athenaeum ; another from Braunton in the Museum of Practical 

 Geology ; and a third from Barnstaple in the Woodwardian Museum. 



BemarJcs. — The first two specimens have been regarded as the Avicula 

 loectinoides , Sowerby,^ but a comparison of the type of that species and M'Coy's 

 description of it with our specimens and with Aviculopeden (Meleagrina) rigida, 

 M'Coy,^ which M'Coy doubtfully identified with it,^ shows that it is quite impossible 

 for them to belong to it. Moreover the third specimen is sufficiently perfect to 

 remove all doubt. 



On the other hand, their likeness to the lengthy series of species referred by 

 Barrande to his genus Panenha is so great that there can remain no question 

 against their belonging to that genus. While, however, their generic position may 

 be regarded as certain, the very vastness of the numbers of species described from 

 Bohemia renders it the more difficult to decide whether our crushed and distorted 

 English shells agree with any of them. At present I know of no Bohemian 

 species with which it seems safe to unite the present form. 



Its chief characteristics seem to be (1) the smallness of the central ribs, five 

 of which occupy the same space as four of the lateral ribs ; (2) the strong, close, 

 thread-like, transverse striae ; and (3) the strength of the ribbing on the latero- 

 superior parts of the shell. 



The Bohemian shell that agrees best with our specimens in the second of these 

 points is Panenlca sjjhseroides, Barrande,* and of it Barrande only figures a single 

 specimen, which is as im23erf ect and distorted as ours. The shell maybe more convex, 

 and the umbo more central and more elevated than it is in ours, but it is impossible 

 at present to decide whether these distinctions are valid, the true shape of neither 

 form being known. 



In P. Bohemica, Barr.,^ and P. domina, Barr.,^ the threading is finer, and the 

 marginal ribbing generally fainter. 



1 1840, Sowerby, ' Geol. Trans.,' ser. 2, vol. v, pt. 3, pi. liv, fig. 2. 



2 1844, M'Coy, ' Synopsis Carb. Toss. Ireland,' p. 80, pi. xiii, fig. 16. 



3 1855, M'Coy, ' Synopsis Brit. Pal. Foss.,' p. 393. 



■* 1881, Barrande, ' Syst. Sil. Bobeme,' vol. vi, pi. cccxxviii, figs. 7 — 10, Et. G. 



» Ibid., pi. Ixxvii, figs. 4, 7—10; pl- xcviii, figs. 2, 1—4; pi. cxxxvii, figs. 1 — 10; pi. cxxxviii, figs. 

 1—22; pi. cxl, figs. 10—12; pi. cli, figs. 19—21; pi. ccliv, figs. 11—13, Et. E; and pi. cccxxxvi, 

 figs. 1—4, Et. G. 6 Ibid., pi. exvii, figs. 7, 8, and pi. cxx, figs. 4, 5, tt. G. 



