84 PERMIAN FOSSILS. 



I have now relinquished the idea of this shell being specifically identical with the 

 Lingula mytiloides of the ' Mineral Conchology,' having examined two original speci- 

 mens of the latter belonging to the cabinet of Mr. J. de C. Sowerby. One of these 

 specimens, which is the original of the figures in the above work, has the margins of 

 its posterior half broken ; the shell is consequently more rounded posteriorly than it 

 is represented. Lingula mytiloides is thus made to approach the form of L. Credneri 

 more than the original figure ; but after carefully restoring the posterior outline of 

 Mr. Sowerby's specimens by continuing the lines of growth, I still found that it was 

 more acuminated at the pedicle end than its Permian congener. Lingula squamiformis, 

 Phill., appears to have a close resemblance to the Geinitzian species. None of my 

 specimens display the posterior median ridge so developed as in those noticed by 

 Dr. Geinitz : probably the more prominent form of this character in the German speci- 

 mens is accidental — perhaps due to lateral pressure. 



Lingula Credneri occurs abundantly, but generally in an imperfect condition, at 

 Thrislington Gap, in the Marl-slate ; and in the same deposit, though more sparingly, 

 at Thickley, and Ferry Hill. Professor Johnstone informs me that he has procured 

 specimens of a Lingula in the underlying Freestone (Rothe-todte-liegende) near Ferry 

 Hill. Dr. Geinitz records its occurrence in the Zechstein of Corbusen, Cosma, and 

 Ilmenau ; also between Konigsee and Unterschoblingen, in Thuringia. 



Family Discinid^, J. E. Gray. 



Diagnosis. — " The upper valve is conical and patelloid, the lower orbicular ; and is 

 attached to marine bodies by a short tendinous pedicle, which passes out through a 

 slit in the hinder part of the disc of the ventral valve."^ 



Genus Biscina? Lamarck, 1818. 



Crania [partim), Schumacher. 

 Orbicula, Auct. 



Diagnosis. — " Testa insequivalvis, ovato-rotundata, depressiuscula ; valvis magni- 

 tudine sequalibus, disco centrali orbiculato utrisque distinctis. Discus valvse superioris 



1 Gray, op. cit., p. 439. 



2 Conchologists are much indebted to Mr. J. E. Gray for his rectifications of some prevailing errors 

 respecting the genus Biscina (vide ' Observations on the Synonymy of the genera Anomia, Crania, Orbicula, 

 and Discina,' in the Annals of Philosophy, new series, vol. x, October 1825 ; and 'On the Arrangement 

 of the Brachiopoda,' in the Annals and Mag. of Nat. Hist., 2d series, vol. ii, p. 439). The genus Crania was 

 established by Retzius on the Nummulus minor of Stobaeus (= Crania Egnabergensis, Retz., := C. striata, 

 Lam.), between 1780 and 1790 ; Poll established the genus Criopus on (the animal of) his Anomia turbinata 

 = Crania ringens, Haeningh., in 1793; Cuvier founded the genus Orbicula on a congeneric form, — the 

 Patella anomala of Miiller, in 1800; and Lamarck instituted, in 1818, the genus Biscina on a shell, which 



