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 LZ. Credneri 
more than the original figure; but after carefully restormg 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 Crednert occurs abundantly, but generally in an imperfect condition, at 
Thrislngton 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 im 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 Discin1p@, J. HK. 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 Discina,? Lamarck, 1818. 
Cranta (partim), Schumacher. 
OrsicuLa, duct. 
Diagnosis.—“ Testa insequivalvis, ovato-rotundata, depressiuscula; valvis magni- 
tudine zequalibus, disco centrali orbiculato utrisque distinctis. Discus valvze 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 Discina (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 Stobeeus (= Crania Egnabergensis, Retz., = C. striata, 
Lam.), between 1780 and 1790 ; Poli established the genus Criopus on (the animal of) his Anomia turbinata 
= Crania ringens, Heningh., in 1793; Cuvier founded the genus Orbicula on a congeneric form,—the 
Patella anomala of Miller, in 1800; and Lamarck instituted, in 1818, the genus Discina on a shell, which 
