POSIDONIELLA. 83 



and referred it to Ambonychia of Hall; but the latter genus is stated to 

 have two cardinal teeth and many lamellar, oblique, diverging, posterior, lateral 

 teeth. 



De Koninck, in giving the diagnosis of the genus for the first time, lays stress 

 on the presence of a " fossette " on the anterior surface below the umbones. 

 This I have termed the " anterior surface " in my description. 



Except in the possession of concentric folds externally, Posidoniella of 

 de Koninck has no real affinity with Posidonomya of Bronn. The latter genus, 

 the type of which is P. Becheri, is characterised by the flatness of its valves, 

 subcentral, inconspicuous umbones, and subcircular form. When Phillips (op. sup. 

 cit.) described the type of this genus he preserved Sowerby's generic appellation, 

 but remarked, " It probably does not belong to Inoceramus, but to Posidonia, 

 Bronn." It was de Koninck, however, who first substituted that name for the 

 genus. Portlock, M'Coy, and Griffith, however, retained the name Inoceramus, 

 M'Coy describing four species from the Carboniferous Limestone of Ireland. 

 Brown retained the name Posidonia, first given by Bronn, who, finding the name 

 in use for a genus of plants, thought it inadmissible for a genus of shells, and 

 substituted Posidonomya. 



I think it very probable that the original of Salter's Anthracoptera Browniana, 

 which he stated to be synonymous with Avicula tenera of Brown (why the specific 

 name was changed is unaccountable), must have belonged to Posidoniella 

 (' Geology of the Country round Wigan,' p. 37, fig. 3). This figure, evidently 

 complete and typical anteriorly, has an outline dotted in to make the shell 

 conform to the type of the then new genus Anthracoptera. 



Whether or no all the members of this genus were byssiferous cannot now be 

 stated, but probably they were. One species, which occurs in the Lower Coal- 

 measures of Lancashire, is known to be so. In such a case the byssal orifice is 

 high up and close under the umbones, at the deepest part of the concavity on the 

 anterior surface. 



It seems to me quite probable that certain of the shells described as Myalina 

 by de Koninck may belong more properly to this genus, but this question must be 

 left until much more material is available for examination. Externally, certain 

 shells of both genera resemble each other closely, and it is necessary to be 

 aware of the hinge-plate and interior to determine certain of the species. 



The genus does not seem to have been limited to the limestone of Car- 

 boniferous age ; but some species, smaller, it is true, than those of the lime- 

 stones, occur in the marine shales of the Coal-measures, and in those which 

 occur below the Millstone-grit of Yorkshire and Lancashire. 



A shell belonging to this genus is described by Meek in the ' Report Geol. 

 Ohio,' vol. ii, " Palseontology," pi. xix, figs. 7 a, b. The description agrees very 



