178 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY.. 



-'A(juJi<^. 



OBSERVATIONS ON THE GENERA ATHYRIS ( = SPIRIGERA), 

 MERISTA, CAMARIUM AND MERISTELLA. 



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

 pean authors have separated the Genera Spirigeea and 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 palaBozoic strata, 

 I have referred to the Genus Spirigera certain species which have a subglobose 

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

 radiating strise; 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 strige, though visible in well-preserved specimens, are still more 

 conspicuous in the partially exfoliated shell. 



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 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^, 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, therefore, the Merista tumida (Dalman) and M. herculea (Barrande) 

 are made the types of the Genus MbristaJ, and the external and internal cha- 



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

 Pal. N.York. 



■j- A specimen from Dudley, England, which does not differ materially from an authentic 

 Swedish specimen ; and Prof .M^Coy has pronounced the Swedish and Dudley specimens identical. 



X In my original observations upon the Genus Camarium, I had supposed that the presence 

 of the strong arching septum in the ventral valve might be incompatible with the existence of 

 internal spires ; but since these spires do exist in M. scalprum, I can have no hesitation in 

 crediting their existence in our Camarium. 



