POSIDONIELLA MINOR. 99 



morden. Staffordshire : in Shales of a similar horizon, Coombes and Swyth- 

 aniley, near Leek. 



Observations. — This species I found to be well known amongst Lancashire collec- 

 tors under the name Posidonia Gibsoni, which was applied by Salter to a shell that 

 he figured, without full description, however, in the ' Survey Memoir on Wigan ' 

 (op. cit.), and Capt. Brown was quoted as the author. I have been unable to find 

 any published account of a species with this name, but Mr. Herbert Bolton, of the 

 Manchester Museum, Owens College, with whom I have discussed the matter, 

 suggests that Capt. Brown was at the time of Salter's publication engaged at work 

 on a series of shells to which the latter had access, and that the name P. Gibsoni 

 was probably a MS. name used on the understanding that Brown was about to 

 publish detailed figures and descriptions. Neither Mr. Bolton nor myself have 

 any hesitation in recognising the shell which is commonly known in Lancashire as 

 P. Gibsoni as the same as that figured by Brown (op. cit.) as Gervillia minor ; and 

 in the absence of any trace of P. Gibsoni, and on the grounds of priority, the 

 specific name " minor " must be retained. The shell in question is very often 

 found crushed in shale, but it appears to have been a flat equivalve form, without 

 any trace of an anterior lobe or ear, and therefore cannot be referred to 

 Gervillia. 



Mr. Salter, when discussing the character of Posidonia Gibsoni in the ' Memoir 

 of the Geological Survey on the Geology of the Country round Wigan,' p. 37, says, 

 " This is evidently not a Posidonia, but it is not yet certain that it belongs to 

 Ambonychia, Monotis, or any of the allied genera, from the want of hinge- 

 characters ; one species has even been given under the names Gervillia minor and 

 G. obtusa in the cabinet of the Manchester Geological Society." 



Salter's figure of the shell at p. 35 of the same memoir is very curious. He 

 gives the shell the shape of a Pecten with a large posterior and short anterior ear ; 

 and in general outline it is very unlike any of the specimens figured by Brown. 

 Mr. George Wild figured a specimen as P. Gibsoni, Brown (Salter), which is now 

 reproduced as typical of Brown's P. Isevis, and which, of course, has no anterior 

 ear. It may have been possible that Salter altered the name P. Isevis to P. Gibsoni, 

 and still gave it as one of Brown's species, just as in the same volume he substi- 

 tuted the name Browniana as a specific title for Brown's Avicula tenua. 



Indeed, it is not at all improbable that Brown's Avicula tenua may belong to 

 the species under discussion ; if so, it would appear to represent a specimen with 

 the periostracum preserved. I have pointed out in my paper on the affinities of 

 Anthracoptera, ' Quart. Journ. Geol. Soc.,' vol. xlix, p. 252, that I thought Salter 

 was in error in referring Brown's shell to his new genus Anthracoptera, as Brown 

 distinctly showed in his figure that in his shell the umbones were anterior 

 and terminal, and that the anterior lobe was obsolete. Salter took it for granted 



