SPIRIFERIDiE. 



115 



nearly straight. There is no regular fold or sinus, but a small depression sometimes exists 

 at and near the front in the ventral valve. Surface smooth, marked by concentric 

 lines of growth, more or less strong at inter\^als. Shell-structure impunctate. Two 

 specimens measured — 



Length 7, width 5, depth 3^ lines. 

 » 5, „ 4, „ 3 „ 

 Obs. Having carefully examined and compared the original example of Terehratula 

 laviuscula. Sow. (in the Museum of the Geological Society), with the American Atrypa 

 nitida, Hall, 1 soon became convinced that Sowerby's specimen was a small and obscure 

 shell, with no definite characters, and therefore should not hold priority over Prof. Hall's 

 well-determined species. Sowerby's specimen possesses the fibrous impunctate shell- 

 stnicture of Athjris or of Meristella ; and in one of these genera it ^^t11, no doubt, 

 requii-e to be classed. I am also somewhat uncertain whether the Bohemian T. Circe 

 of Barrande be more than a variety of the shell under description; but, as there 

 may exist still some uncertainty about the matter, and as I have not had the 

 advantage of being able to examine many specimens of these shells, I will describe this 

 last under a separate head, while repeating that our British examples attributed to 

 Barrande's species seem to pass by so many gradations into 31. niiida, that it is 

 possible they are all variations of a single species. The only difierence I can 

 observe in the two is, that in M. Circe there appears to exist a small but deepish 

 sinus towards the front in the dorsal valve of many specimens, which gives to the frontal 

 line an elevated convex curve ; but this is also visible, to a lesser degree, in many examples 

 of undoubted J/, nitida; and in his description oi Atrypa nitida, Prof. Hall does not 

 fail to observe that " the dorsal valve (our ventral) is sometimes marked, near the base, 

 by a longitudinal depression." I had noticed the presence of spirals in 1847, and 

 recorded the observation in the ' Bulletin Soc. Geol. France and Lindstrom has also 

 detected them in a Gothland specimen. In his description of A. nitida. Prof. Hall 

 observes : — " It is usually remarkable for its smooth surface, interrupted only by a few 

 hnes of growth on the middle or towards the base, the finer concentric striae being 

 obsolete or invisible to the naked eye. In some individuals the shell becomes thickened 

 near the base [front], and marked by very strong lines of growth." 



Position and Locality. Meristella nitida occurs in the AVenlock Limestone and 

 Shale at the Rushall Canal near Walsall, at Dudley, Benthall Edge, at Tynewydd, Llan- 

 dovery (the original locality), in "Wenlock Shale. In Ireland it has been found by the 

 Geological Survey in the Upper Silurian at Cahirconree, on the west side of County 

 Kerry. It occurs also in Gothland. In America, according to Prof. Hall, it is found in 

 every part of the Niagara group of New York State, being most abundant at Lockport ; 

 also at "Wolcott, in "^"ayne County, &c. 



