ANIMALS. 161 



Mytilus septifer, King. Plate XIV, figs. 8, 9, 10, 11, 12, 13. 



MoDiOLA ACUMINATA,! J. de C. Sow. Trans. Geol. Soc. Lond., 2d series, vol. iii, 



p. 119, 1829. 



— _ „ De la Beche, 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. 



— — „ Morris, Catalogue, p. 91, 1843. 



Mytilus septifer, King, De Verneuil, Bull. Soc. Geol. de France, 2"* serie, vol. i, 



p. 32, 1844. 

 OsTEEA ? PUsiLLA (young), King. Op. cit., p. 34. 

 Mytilus septifee „ Geol. Russ., vol. i, p. 224, 1845. 



OsTREA PUSILLA (young), „ Op. cit., p. 225. 

 (?) Mytilus Hadsmanni, Goldfuss. Keyserling, Petschora-land, p. 260, pi. xiv, figs. 2, 



2 a, 1846. ' 



— SEPTIFEE „ Tennant, Strat. List., p. 88, 1847. 



— — „ King, Catalogue, p. 10, 1848. 

 OsTEEA ? Tayloriana (young), King. Op. cit. p. 9. 



Mytilus squamosus, J. de C. Sow. Howse, Trans. T. N. F. C, vol. i, p. 248, 1848. 

 (?) — Hausmanni, Goldfuss. Geinitz, Versteinerungen, pi. iv, fig. 14, 1848. 



Diagnosis. — Inequivalve : tumid : rhomboidal marginally, the hinge line being 

 slightly oblique (in old specimens) to the anterior and posterior margins : three quarters 

 of an inch long, and half an inch wide : with foliaceous laminae of growth. Vmhones 

 ecurved at the point. Vmhonal cavities, each with an oblique plate serving as a 

 falcrura for the anterior adductor muscle. 



" This species, a shorter and wider one than the last, is lobed in front like a Modiola, 

 and furnished with a ridge that posteriorly bounds the anterior adductor muscular 

 impressions."^ 



The form of Mytilus septifer varies with age, young specimens being more oblique 

 and narrower than old ones. It was this circumstance that led me into the error of 

 considering some single valves of very young individuals to belong to a distinct shell, 

 which I named in my ' Catalogue' Ostrea ? Tayloriana. The ridge or plate in the..umbonal 

 cavities is also somewhat variable, being more oblique when the shell is young than when 

 it is old ; but in both cases, although it " posteriorly bounds the anterior adductor 

 muscular impressions," it has obviously served as a fulcrum for the producing muscle.^ 



1 Mr. Sowerby's specific name having been anticipated by Schlotheira's Mytilites acuminatus, for 

 another shell, it has been deemed necessary to employ that of septifer for the present species. 



® King, Catalogue, p. 10. 



3 It is difficult to represent the anterior adductor muscular impressions on casts, as the curving of the 

 umbones prevents their being properly seen: the impression a, in fig. 11, PI. XIV, ought to have been 

 placed much further forward, where in fact it cannot be represented in the figure. 



V 



