20 BRITISH DEVONIAN BRACHIOPODA. 



Genus — Merista, Suess. 

 Mkhista plebeia, Sow. (sp.), 1837. PL III, tigs. 2 — 10. 



Atkypa plebeia, Sow. Trans. Geol. Soc, 2 ser., vol. v, pi. hi, figs. 12, 13. 



— lacryma, Sow. Ibid., fig. 9. 

 Terebratula subcurvata, Minister. Beitrage, Heft 3, pi. 14, figs. 4, 5, 0. 

 Spirifera flebeia, Phillips. Pal. Fossils of Devon, Cornwall, &c, p. 70, pi. xxviii, 



fig. 121, 1841. 

 Spirigera plebeia, D'Orbigny. Prodrome, vol. i, p. 99, 1849. 



Terebratula scalprum, Roemer. Das Rheinisch. Utbergangsgeb., p. 68, pi. v, fig. ', 



1844. 



Spec. Char. Shell transversely obovate, as wide as or a little wider than long ; valves 

 moderately convex, with a slightly elevated wide mesial lobe or fold, apparent only near 

 the front of the dorsal valve ; a shallow sinus or depression is visible in the- corresponding 

 portion of the ventral one ; beak small, very much incurved ; external surface marked with 

 close contiguous lines of growth ; proportions variable ; two examples have measured — 



Length 9, width 10, depth 5 lines. 

 10 1 



11 lyJ > 11 "I* 11 U 11 



Obs. This common species is very variable in shape, some specimens being wider than 

 long, whilst others are longer than wide. It is usually almost circular, the mesial 

 fold never attaining much projection or elevation. Alrypa lacryma, Sow., of which the 

 original type is preserved in the Museum of the Geological Society, along with the types 

 of A. plebeia, appears to belong to the same species as the shell under description, for we 

 find every intermediate shape uniting them. The generality of specimens have not their 

 outer shell-surface perfect ; and consequently a longitudinal line is seen to extend along 

 the smaller or dorsal valve from the umbo to half or more of its length, denoting 

 the presence of an interior septum, while two diverging lines extend from the extremity 

 of the beak to about two thirds of the length of the valve, indicating the presence of large 

 condyle-plates, to which are fixed the transverse plates, or shoelifter-shaped process, while in 

 some examples the portion of the matrix between the hinge-plates has dropped out, leaving 

 a triangular hollow in the shell or cast, as seen in fig. 5. 



M. plebeia occurs abundantly in the Middle Devonian limestone of Mount Wise and 

 Stonehouse Hill, near Plymouth ; at Barton and Lunmiaton, near Torquay ; Ramsleugh 

 Quarry, near Ogwell ; Woolborough, near Newton Abbot; and at Hagginton Hill, near 

 Ufracombe, in Devonshire. On the Continent it occurs at Gerolstein, in the Eifel ; at 

 Elbersreuth, &c. 



