No. 89.] 



73 



Geological relations. The single species known occurs in the Hamilton group, 

 associated with other Brachiopoda, but extremely restricted in its vertical range. 



OBSERVATIONS ON THE GENERA ATHYRIS ( = SPIRIGERjl), 

 MERISTA ( = CAMARIUM), MERISTELLA AND LEIORHYN- 

 CHUS. 



Among- the fossils referred for many years to Terebratula, Atrtpa, etc., 

 European authors have separated the Genera ATHTRisaud Merista; shells which 

 have many characters in common, and which were indeed at first united under 

 Spirigera or Athtris, until in 1851 the Genus Merista was proposed by Prof. 

 SuESS. In my later studies of the Brachiopoda of the American palaeozoic strata, 

 I have referred to the Genus Athyris certain species which have a subglobose or 

 ovoid form, with lamellose surfaces, and without, or with scarcely perceptible 

 radiating strige; 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 Marista ( Atrypa ) tumida, Dalm an, but are less ventricose : 

 they all have internal spires, and, when perfect, the beaks appear to be imperforate. 

 The radiating striee, though visible in well-preserved specimens, are still more 

 conspicuous in the partially exfoliated shell. Atrypa tumida of Halman is cited 

 by Davidson as one of the types of the Genus Merista. 



I proposed last year* a separation of certain Merista-like forms, under the name 

 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 this arching septum, in its attenuation towards the beak, is identical with 

 the shoelifter process described as belonging to the Genus Merista. An examina- 

 tion 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 in- 

 habitants 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. tumida1[, 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 characters marking 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, in the most solid of the spe- 

 cimens which I possess, readily reveals the presence of the septum. 



Since this shoelifter process, or septum, was originally described by Prof Suess 

 as characteristic of his Genus Merista, and the species designated by him as the 

 types of this genus ( the M. scalprum and M. hercuUa of Barrande ) "do 



* In the twelfth Report of the Regents on the State Cabinet : Also Supplement to Vol. iii, 

 Pal. N.York. 



] A specimen from Dudley, England, which does not differ materially from the authentic 

 Swedish specimen; and Prof. M«Coy has pronounced the Swedish and Dudley species identical. 



[Senate, No. 89.] 10 



