104 CARBONIFEROUS LAMELLIBRANCHIATA. 



Non Mxalina, Kirkby, 1880. Quart. Journ. Geo!. Soc, vol. xxxvi, p. 585. 

 — — Barrois, 1882. Terrains anciens Asturias et Galice, p. 336. 



— Walcott, 1884. Monogr. IT. S. Geol. Surv., vol. viii, p. 237. 



— Etheridge, 1888. Brit. Foss., vol. i, Pala3oz., p. 28(5. 

 Mttilus, Etheridge, 1888. Ibid., p. 287. 



Mtalina, de Koninck, 1885. Jaune Calcaire Carbonif. Belgique, p. 1G8. 

 Mttilaeca (Mytilus), de Koninck, 1885. Ibid., pp. 180, 279 ; explicat., pi. xxix, 



figs. 22 and 26. 

 Myalina, Miller, 1889. North American Geology and Palaeontology, p. 492. 



— Whidbornx, 1891. Monogr. Devonian Fauna S. England, p. 45. 



Generic Characters. — Shell of variable size, more or less triangular in shape. 

 Anterior end obsolete. Shell oblique and strongly bent at anterior border, so 

 that a more or less flattened anterior surface is formed. The posterior part of the 

 shell alate, compressed, and expanded. Umbones pointed and terminal. Cardinal 

 border straight. Hinge-plate much thickened, and longitudinally striated ; the 

 number of striae greater in front than behind. The anterior adductor scar is 

 situated on a shelf or hollow on the inner edge of the plate, just below the junction 

 of the hinge-plate and anterior margin, which is here much thickened. The 

 posterior adductor scar is very large and oval. The mantle-line is entire, and 

 placed at some distance from the edge of the shell. Cartilage inserted in the 

 hollows between the stria? of the hinge-plate. The lines of growth are well marked 

 and often imbricate or lamellar. 



Observations. — This genus was established in 1842 by de Koninck (' Anim. 

 Foss. Carbomf. Belgique,' p. 125) for certain Mytiliform shells which possessed a 

 striated hinge-plate, and had the anterior adductor muscle inserted on a little 

 septum within the beaks. The acutely bent shell and flattened anterior surface, 

 though not particularly mentioned, are probably included under the expression 

 " La forme exterieure du genre Myalina ressemble assez bien a celle des Mytilus." 

 De Koninck then describes three species of this genus — 



Myalina Qoldfussiana. M. lamellosa. M. virgula. 



M'Coy, writing two years later, did not recognise the genus ; a fact easily 

 accounted for, as he had no interiors, and he referred two species — Myalina 

 Flemingi and M. compta 1 — to Mytilus ; and one — Myalina Vemeuilii — to Avicula. 



King, when discussing the generic affinities of the Permian representatives of 

 this genus, notes that these have the umbonal plates and striated hinges of 

 Myalina ; but, as he thought that the Coal-measure shell Naiadites was indicated 

 by de Koninck's description, and believing that " these were all fresh- or brackish- 

 water shells " (one is seemingly warranted in characterising Myalina as a fresh- 



1 1 consider that M.. compta, M'Coy, is only a varietal form of M. Vemeuilii. 



