MYALINA PERNOIDES. 117 



M. pernoides corresponds to Naiadites carinata, being obliquely U-shaped. 

 Myalina lamellosa corresponds to Naiadites triangularis, with a short hinge-line, 

 but with transversely triangularly produced shell ; and Myalina peralata has the 

 quadrate character of Naiadites quadrata. Whether these four forms of each 

 genus are strongly marked varieties, or easily recognisable species, is a moot 

 point ; but, as in the case of the four species of Naiadites, I have with Myalina 

 retained the specific names. 



The Scotch specimens are all much smaller than the type, and have the anterior 

 lobe less well marked, though undoubtedly present. 



There appears also to have existed a variety of this species, which was much 

 more gibbose than the type specimens of this form, and which are figured on 

 PI. IV, figs. 5 and 6. This would appear to be a cross between M. Flemingi and 

 M. Verneuilii, having the expanded form of the latter and the broad anterior 

 surface of the former. All three forms seem to have been present together in the 

 beds at Garngad Road, Glasgow. 



Myalina pernoides, Portloch, sp., 1843. Plate IV, figs. 1, 2. 



Inocebamus pebnoides, Portloch, 1843. Eeport Geology Londonderry, &c, 



p. 567, pi. xxxviii, fig. 5. 



— Morris, 1843. Catalogue of British Fossils, p. 111. 



— — — 1854. Ibid., 2nd edit., p. 170. 

 Aviculopecten ellipticus, Baily, 1884. Explanat. Sheet 26, Geol. Surv. Map 



of Ireland, p. 28. 

 Inoceeamus peenoides, Etlieridge, 1888. British Foss., vol. i, Palaeoz., p. 274. 



Specific Characters. — Shell rhomboidal, obliquely extended in a dorso-ventral 

 direction, of moderate size, moderately gibbose in front and above, but elsewhere 

 compressed, flattened, and expanded. The anterior border is very long and 

 almost straight ; it may be slightly concave about the junction of the anterior 

 and middle thirds. The inferior border is bluntly but regularly curved, the 

 anterior limb of the curve being the more obtuse and extending further down- 

 wards than the posterior. The posterior border is much shorter than the anterior, 

 and obliquely truncated downwards and backwards, gently convex, having a 

 general direction almost parallel to the anterior border; it makes an obtuse 

 angle with the hinge-line above, and passes with a gradual curve into the 

 inferior border below. The hinge-line is straight and short, about equal in 

 length to any diameter of the shell parallel to it. The umbones are pointed, 

 convex, and terminal, not contiguous. From these a narrow, oblique swelling 



