114 



SUPPLEMENT TO THE 



13. Atrypa Barrandei, Dav. 



sp. Sil. Mon., PL XIII, figs. 10 to 13; Sil. Sup., PI. 

 VII, figs. 7, 7 a, 7 b. 



Eetzia? Barrandi, Bav. Sil. Mon., p. 128, 1869. 



Atrypa Barrandei, Dav. Geol. Mag., New Series, vol. viii, January, 1881. 



During an excursion I made near Walsall in 1847 1 picked up several specimens of 

 the small species under description. Knowing nothing of its interior characters, I 

 provisionally described it as a Terehratula, but subsequently I thought it might be refer- 

 able to Betzia, on account of Dr. Lindstrom having found that the shell was possessed of 

 spiral coils. In 1879 Professor James Hall, at p. 162 of the 'Twenty-eighth Annual 

 Report of the New York State Museum of Natural History of New York,' states that the 

 B. Barrandei seems to be very closely related if not identical with his Ccelosjnra 

 disparialis ; and in the same year M, Barrande, in the fifth volume of his magnificent 

 work on the ' Silurian Fossils of Bohemia,' describes T. Barrandei as a species of Athyris, 

 but in his figure represents it with the spiral coils of an Atrypa. 



It was, however, left to Mr. Glass to entirely investigate and determine the internal 

 characters of this species, so abundant and characteristic of the Wenlock Shales of 

 Shropshire. The shell in size does not exceed four lines in length and the same in 

 breadth, by three in depth, with nearly a flat or even slightly concave dorsal valve (see 

 'Sil. Mon.,' PI. XIII, fig. 10 to 13). Still, notwithstanding its small dimensions, after 

 great trouble Mr. Glass has succeeded in completely exposing in four specimens 

 its spirals and their connecting process. These in the main agree pretty closely, 

 although differing slightly in detail, with those of Atrypa marginalis ; and Mr. Glass's 

 specimens show that soon after the principal stems of the spirals leave their attachment 

 to the hinge-plate they give oS" a V-shaped lamella, by which they become connected, as 



in Atryjm. 



The principal coils, however, are not quite 

 level, as in Atrypa, the two inner sides of 

 these coils being slightly higher than the two 

 outer sides and turned towards the margin of 

 the shell. The ends of the spires curl over to 

 meet each other, but the amount of convexity 

 of the spirals on the side facing the bottom 

 of the dorsal valve is very slight, because 

 and this shghtness of convexity is necessitated 



Atrypa 'Barrandei. Spira developed by Mr. Glas 



there are but four or five convolutions 

 by the very small depth of the valve. 



I therefore believe that the spiral arrangement in A. Barrandei is only a slight modifi- 



