﻿ACTINOPTERIA. 



69 



contact is in the Torquay Museum, and, while the surface of its right valve is in 

 a fair state of preservation, that of its left valve is almost entirely destroyed, so 

 that all that can be asserted is that it agrees with the other specimens of the left 

 valve in general shape. It shows that the right valve is slightly flatter than the 

 left, and that its umbo is a little more central. 



The specimen shown at PI. VIII, fig. 7, has caused me some perplexity. I 

 believe, however, that it is a specimen of the present shell, obliquely set in the 

 matrix, and with the finer ornamentation of its surface weathered away. 



Affinities. — Both valves of this shell bear great likeness to the two valves of 

 Avicula troglodytes, Goldfuss MS., 1 thus supporting the presumption of their 

 own identity ; the likeness even extends to the existence of the minute threads, and 

 to the nearly equal depth of the two valves, so that the German species is 

 evidently a very near relation. It seems, however, to be specifically distinguished 

 by its shape, being a much less oblique shell, and having longer and more defined 

 wings and more arching margins. Freeh 2 refers Follmann's species to his group 

 of Avicula Wurmii. 



Pterinea Mneata, Goldfuss, 3 with which Freeh * unites Ft. elongata, Goldfuss, 5 

 and Pt. plana, Goldfuss (pars), is also very similar in ornament, but has a very 

 much smaller anterior wing, a more defined and generally much longer posterior 

 wing, and a more sigmoid posterior margin. 



Avicula expulsa, Barrande, 6 approaches our shells in shape, but its ribs are 

 finer and not alternating, its transverse markings are much fewer and coarser, and 

 its front ear is more truncated. 



A. urbana, Barrande, 7 is much too fragmentary for identification. Its ribs do 

 not alternate, and show no transverse markings, and its shape seems broader. 



The right valve of Avicula tumida, F. A. Romer, 8 seems to be much more 

 produced in front, and to have a much smaller wing. 



1 1885, Follinann, ' Verh. Nat. Hist. Vereins preuss. Eheinl.,' vol. xlii, p. 202, pi. iii, figs. 6, 

 6 a, 6b. 



- 1891, Freeh, ' Abhandl. Geol. Specialk. Preuss.,' Band ix, pt. 3, p. 40, pi. iii, fig. 5. 

 3 1834-40, Goldfuss, ' Petref. Germ.,' vol. ii, p. 135, pi. cxix, figs. 6 a — c. 

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



5 Ibid., p. 135, pi. cxix, figs. 4a—/. 



6 1881, Barrande, ' Syst. Sil. Bohome,' vol. vi, pi. ccxviii, figs. 13, 14. 



7 Ibid., pi. ccxix, fig. 6, i, 2. 



? 1860, P. A. Eomer, ' Beitr.,' pt. 4, p. 161, pi. xxv, fig. 7. 



