CARBONIFEROUS BRACHIOPODA. 
283 
A. glohdaris and A. amhigua are from the Limestone of Vise, and are found principally 
in Scotland and in the centre of England, and are hardly known out of Great Britain and 
Belgium. 
21. Athyris ambigua, Soio. Dav., Garb. Mon., p. 77, PI. XV, figs. 15 — 26; Sup., 
PI. XXXIV, figs. 10, 11. 
Athp-is amhigiia is a very variable shell, both with respect to breadth and length. A 
remarkable variety of the shell, which we figure in PI. XXXIV, fig. 10, of this Supple- 
ment, differs from the ordinary form by its mesial fold being much produced, and by its 
having on the ventral valve a wide, deep, flattened sinus, the edges of which are somewhat 
pinched upwards into a narrow rounded fold, which slopes gently outwards. 
This species, of which I have seen several specimens, was found by Mr. John Young in 
the Carboniferous Limestone Shales at Gorrie Burn, Campsie, near Glasgow, and by Mr. 
J. Neilson, junr., in a section opened in the same formation in the Garngad Road, 
Glasgow. 
In his paper " On the Geology of the Campbeltown District " (' Trans, of the GeoL 
Soc. of Glasgow,' vol. ii, pi. ii, fig. 2, 18G3), Mr. James Thomson observes that upon the 
shore at Machrahanish Bay numerous specimens of Atliyris amUgua are found at the 
junction of the Limestone and Sandstone, and that in several examples the shell is 
marked with faint longitudinal striae. 
Genus Retzia, King. 
22. Retzia carbonaria, Bav. Carb. Mon., p. 219, PL LI, fig. 3 ; and Sup.^ 
PI. XXX, fig. 16. 
This is seemingly an uncommon species in our British Carboniferous Rocks. A 
couple of specimens have been recently discovered by Mr. Widborne in Carboniferous 
Limestone Shales close to the Black Rock Quarry, near Bristol,^ and one of these I here 
figure. 
^ Thanks to Mr. G. F. Widborne I have been able to examine the following species from the Bristol 
district : 
Bristol. — Millstone-grit — Produclus seahriculus. 
Avon section. — Lower Limestone Shales — Terebratnla hastata, Athyris Roi/ssii, A. globularis, Retzia 
37 
