ANIMALS. 159 



cavity.^ Dr. de Koninck has described a genus under the name of Myalina^ which 

 is perhaps the proper receptacle for these shells ; but I am averse to placing them 

 in it, in consequence of there being one or more Neocomian inequivalved Mussels 

 (e. g. Mytilus inaquivalvis), and some recent species {M. bilocularis, &c.) with umbonal 

 trarisnerse plates? Perhaps there are some true Mussels in which the cartilage is 

 exposed, and placed in a furrow, as in the two Permian species. The latter have 

 the cartilage-plates or fulcra parallelly grooved as they are in Myalina (vide PL XIV, 

 fig. 13). The Mytilus crassus, Fleming, belongs to De Koninck's genus; and all the 

 modioliform shells described by J. de C. Sowerby in Mr. J. Prestwich's Memoir ' On 

 the Geology of the Coal-field of Coalbrook Dale' (vide Trans. Geol, Soc. Lond., 2d 

 series, vol. v, PI. XXXIX, figs. 10, 15 — 18), appear to be congeneric species. As I 

 strongly suspect these were all fresh- or brackish-water shells, one is seemingly 

 warranted in characterising Myalina as a fresh-water genus. The next question for 

 consideration is, whether it possessed any marine species. If the Permian forms 

 belong to De Koninck's genus, — Myalina, like some other genera, may be said to 

 contain both kinds, as they were undoubtedly oceanic shells. 



Mytilus squamosus, /. de C. Sowerby. Plate XIV, figs. 1, 2, 3, 4, 5, 6, 7. 



Casts of bivalves resembling muscles. Winch. Trans. Geol. Soc. Lond., vol. iv, 



p. 10, 1817. 

 (?) Mtttlus, N.S., Phillips. Phil. Mag., vol. iv, p. 403, 1828. 



— SQUAMOSUS, J. de C. Sow. Trans. Geol. Soc. Lond., 2d series, vol. iii, p. 



120, 1829. 



— — „ De laBeche, GeoL Man., p. 385, 1831; Germ. 



Transl., p. 459, 1832; 3d Eng. ed., p. 573, 

 1833. 



— — „ Phillips, Encyc. Met., vol. iv, p. 616, 1834. 



— — „ Thomson, Outlines of Min. Geol. &c., ' vol. ii, 



p. 316, 1836. 



— Hausmanni, Goldfuss. Petrefacta, part ii, p. 168, pi. 138, fig. 4, 1837. 



— actjminatus, «7. de C, Sow. Phillips, Lardner's Cyclop., Geology, vol. i, p. 



190, fig. 2, 1837. 

 Gekvillia, Geinitz, Leonhard u Bronn's Neues Jahrbuch, p. 639, 1841. 



Mytilus squamosus, J. de C. Sow. Morris, Catalogue, p-. 93, 1843. 



^ The situation of the anterior adductor muscle is shown by the cast of the space intervening the 

 horizontal plates (that is, the prolongation between the umbones in the cast represented in Plate XIV. fig. 5) 

 displaying its impressions : these are seen on the prolongation ; but they cannot be represented in the 

 figure. Through an oversight, the impression marked c in fig. 7, PI. XIV, is referred to the anterior adductor 

 muscle in the explanation appended to the plate : it ought to have been named the impression of the anterior 

 visceral or pedal muscle. 



* Description des Animaux fossiles, qui se trouvent dans le terrain carbonif^re de Belgique, p. 125. 



' The genus Dreissina, being a fresh-water group, is not taken into consideration. 



