14 BRITISH DEVONIAN BRACHIOPODA. 



Athyris concentrica, Von Buck (sp.), 1839. PI. Ill, figs. 11 — 15, and 24. 



Terebratula concentrica, Von Buck. Ueber Terebrateln, p. 103, Berlin, 1834 ; and 



Mem. Soc. Geol. France, vol. iii, p. 214, 1839 (described, 

 but not figured). 



without or with scarcely perceptible radiating striae; while other forms, which are less distinctly lamellose, 

 and always more or less distinctly radiatingly striate, with fine concentric lines of growth, I have referred 

 to the genus Merista. Many of the latter have the general form and surface-characters of Merista 

 {Atrypa) tumida, Dalman, but are less ventricose ; they all have internal spires, and when perfect, the 

 beaks appear to be imperforate. The radiating striae, though visible in well-preserved specimens, are still 

 more conspicuous- in the partially exfoliated shell. Atrypa tumida of Dalman is cited by Davidson as one 

 of the types of the genus Merista. 



"I proposed last year (' Twelfth Report of the Regents') a separation of certain Merista-like forms 

 under the name of Camarium, on account of the presence of an arching transverse septum in the ventral 

 valve. Subsequently a more careful consideration of the characters of Merista, as given by Mr. Davidson, and 

 an inspection of his figures, have shown me that the arching septum, in its attenuation towards the beak, is 

 identical with the shoelifter process described as belonging to the genus Merista. An examination of numerous 

 specimens of different species of those which I have referred to the genus Merista shows no evidence of 

 this process or septum, and the deep muscular impression below the rostral cavity, and the thickening of 

 this part of the shell, are characters incompatible with the existence of the septum. Moreover, I conceive 

 that this arching septum, or the extension of the shoelifter process into the cavity of the valve, would 

 produce such a modification of the soft parts of the animal, that the inhabitants of these shells were 

 generically distinct from the inhabitants of the large uninterrupted cavity of the shells which heretofore I 

 have referred to Merista. 



"In order, if possible, to reach a solution of the question, I have had the shell removed from a solid 

 specimen of M. tumida (from Dudley), which is one of the types of the genus, and there is certainly no 

 evidence of the septum or shoelifter process, but, on the contrary, the presence of all the character- 

 markings of the American species which I have referred to Merista, in vol. iii, 'Pal. New York.' At the 

 same time, the Merista {Terebratula) scalprum of Barrande \_Herculea of Barrande, or scalprum of 

 Roemer], in the most solid of the specimens which I possess, really reveals the presence of the septum. 



" Since this shoelifter process, or septum, was originally described by Professor Suess as characteristic of 

 the genus Merista, and the species designated by him as the types of the genus (the M. scalprum and 

 M. Ilercidea of Barrande) ' do possess this feature, the genus must be retained for the species with the 

 shoelifter process.' (Davidson.) 



" It would appear, therefore, that the genus Camarium, proposed by me in the preceding report, 

 possesses characters identical with Merista, as originally described by Suess, but which have been over- 

 looked to some extent in consequence of the reference to M. tumida as a typical form of the genus 



At the same time, as the M. tumida of Dalman, an English and Swedish species, in common with numerous 

 well-marked forms in our Silurian and Devonian strata, do not possess this feature, we can no longer with 

 propriety refer them to that genus. 



"With this restriction, the Meristce proper consist of smooth, ovoid, circular, or transverse shells, 

 with usually a conspicuous sinus upon the ventral valve, and a corresponding wide, often undefined, mesial 

 fold or elevation upon the dorsal valve ; the hinge-articulation being not very different from that of Athyris, 

 to which they are allied. 



"The interior of the ventral valve, however, is strongly distinctive, and the septum or shoelifter process 



