MYALINA PERALATA. 119 



The second specimen I figure was obtained by Mr. John Dunn, who has for 

 many years collected from the fossiliferous beds of the Redesdale district ; and I 

 am indebted to him for permission to figure and describe it. 



This specimen occurred in shale, and consists of a left valve, one portion of 

 the slab showing a fine cast of the exterior. The shell itself has somewhat dis- 

 appeared, but faint traces of the striated hinge-plate and of the anterior adductor 

 muscle-scar are to be seen. 



This shell cannot be mistaken for any other, its great dorso-ventral extension 

 and moderate convexity being characteristic of the species. The anterior portion 

 of the shell is not so completely absent as in some members of the genus, owing 

 to the angle made by the two portions of the shell at the ridge being greater 

 than usual. 



The Naiadites (Anthracoptera) quadrata, Sow., sp., has somewhat the same 

 form as M. pernoides ; but it is less oblique, and in large examples much more 

 transverse relatively; and it possesses a trifid anterior muscle-scar, situated 

 within the umbo. 



Myalina Vemeuilii is more transverse and not so extended downwards, 

 though of all the species in the genus it has the greatest affinity to the one under 

 description. 



In the original description of Myalina pernoides, by Portlock, he says, "Beak 

 slightly curved, and an obscure ridge extending to the margin." 



Portlock speaks of another shell, somewhat akin to his Inoceramus pernoides, 

 for he says in his remarks on that species, " The Derryloran shell is more gibbous 

 and incurved, and may be called I. gryphus." Of this I can at present find no 

 trace. 



Baily, in the palaaontological notes to the Explan. Sheet 26 (1844), Geol. 

 Survey of Ireland, at p. 27, considers Inoceramus pernoides of Portlock to be a 

 synonym of Aviculopecten ellipticus ; but in this fact he must be mistaken, the 

 shell having no affinity at all to that genus. 



Myalina peralata, de Eoninclc, 1885. Plate IV, figs. 11, 12; Plate VI, 



fig. 26; Plate VII, fig. 8. 



Myalina peealata, de Koninck, 1885. Faune du Calcaire Carbonifere de la 



Belgique, p. 172, pi. xxix, figs. 5, 12, 13. 



Specific Characters. — Shell obliquely U-shaped, produced downwards, mode- 

 rately and regularly convex. The anterior surface is less flattened than in other 

 species, and the end formed by the junction of the valves is prominent, forming 



