GENUS MERISTELLA. 295 



Genus MERISTELLA* (Hall). 



This genus was described in the Thirteenth Report on the State 

 Cabinet in 1860, for shells which had heretofore been included under 

 the genus Athyris and subsequently under Merista. Differing from 

 Athyris, they possess the general external form and characters of Merista, 

 but have not the internal septum so characteristic of the latter genus.f 



• Sec note on page 297. 



t In discussing the relations of this group of shells with Athtbis and Merista above cited, I 

 have made the following observations : 



Among the fossils referred for many years to Tkrebratl'la, Atrtpa, etc., European authors have 

 separated the Genera Atuvris and Merista; shells which have many eharacters in common, and 

 which were indeed at first united under Spirigera or Athyris, until in 1851 the Genus Merista was 

 proposed by Prof. Stess. In my later studies of the Brachiopoda of the American paleozoic 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 strisa ; 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. JIany of the latter have the general form and 

 surface characters of Merista (Atrifpa ) lumida, Dalman, but are less ventricose : they all have inter- 

 nal spires, and when perfect, the beaks appear to be imperforate. The radiating stria;, though visible 

 in well preserved specimens, are still more conspicuous in the partially exfoliated shell. Atn/pa tumida 

 of Dalman is cited by Davidson as one of the types of the Genns Merista. 



I proposed last year (Twelfth Report on the State Cabinet) a separation of certain Mcrista-Iike 

 forms, under the name Camabium, 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 attenu- 

 ation 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 impres- 

 sion 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 those of the large 

 uninterrupted cavity of the shells which I have heretofore 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, England), 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 (Terebratida) scalprum of Barrandb [JVi. herculea of Barrande, or 

 M. scalprum of Riemer], in the most solid of the specimens which I possess, readily reveals the 

 presence of the septum. 



