120 



BRITISH SILURIAN BRACHIOPODA. 



Meristella? subundata, M'Coi/ (sp.). PI. XIII, figs. 4, a, b, c. 



Hemithyeis subundata, M'Coy. Brit. Pal. Foss., p. 207, pi. in, 1852; and Annals 



Nat. Hist., 2nd series, vol. viii, p. 394, 1851. 

 Rhynchonella — Salter. Siluria, 2nd edit., p. 545, 1859. 

 Hemithyris — Schmidt. Archiv Naturk. Livlaiids, &c., vol. ii, p. 214, 1858. 



Sj)ec. Char. " Transversely broad-oval ; valves almost equally convex ; beak very 

 small, apicial angle 140° near the apex; lateral margins straight; front raised into a 

 rounded wave, from which in the large valve a wide shallow mesial depression extends 

 half-way to the beak, with a corresponding elevation in the small valve in some specimens 

 extending to the beak." Length 11, width 15 lines. 



Obs. I have reproduced Prof. M'Coy's diagnosis and figures, as he had greater 

 opportunity of studying the shell than I have had ; but I have ventured to remove it from 

 Hemithyris, as its affinities appear to me to tend more towards those of the Athyrida 

 than to the BhynchonellidcB, of which the term Hemithyris is no more than a synonym. 

 In this alteration I am supported by Mr. Salter, who has devoted so much attention 

 to the British Pala30zoic genera and species. The shell is smooth, and remarkable for 

 the smallness of its beak. It is not much unlike some compressed examples of Meristella 

 tumida. 



Position and Locality. It is stated to be very common in the schists and limestones 

 of Mathyrafal, South of Meifod, Montgomeryshire; also in the slate of Alt-ffair-ffynnoii, 

 LlanfyUin ; and at p. 545 of 'Siluria' it is quoted from the Llandovery rocks. At p. 275 

 of vol. iii of the ' Memoirs of the Geological Survey,' its locality is more exactly given 

 by Mr. Salter as Pen-y-craig, Llangynyw, near Mathyrafae, Meifod, North Wales (in 

 the Lower Llandovery). Prof. P. Schmidt mentions having found this species in the 

 Lower Silurian of Baltischport. 



Genus Athyris, J/'Coy (= Spirigera, D'Orbiyny). 



For the characters of this genus readers are referred to my ' Monograph of British 

 Permian Brachiopoda/ p. 20, &c., and to the 'Devonian Monograph,' p. 113, &c. 



Although the genus Merista proper, with its shoe-lifter-shaped plate, is represented 

 abundantly in the Upper Silurian rocks of Bohemia, I am not (as before said) at present 

 acquainted with any British Silurian species that I could refer to that genus. 



