ANIMALS. 161 
MYTILUS SEPTIFER, King. Plate XIV, figs. 8, 9, 10, 11, 12, 13. 
Mopiona acumrinata,! 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. 1i, 
p. 316, 1836, 
res — a Morris, Catalogue, p. 91, 1843. 
Myrtitus spprirer, King. De Verneuil, Bull. Soc. Géol. de France, 2™° série, vol. i, 
p. 32, 1844. 
OsTrna ? PUSILLA (young), King. Op. cit., p. 34. 
MyTILUS SEPTIFER » Geol. Russ., vol. i, p. 224, 1845. 
OsTREA PUSILLA (young), _,, Op. cit., p. 225. 
(?) Myritus Hausmanni, Goldfuss. Keyserling, Petschora-land, p. 260, pl. xiv, figs. 2, 
2a, 1846. : 
— SEPTIFER ny Tennant, Strat. List., p. 88, 1847. 
— — es King, Catalogue, p. 10, 1848. 
Ostrua ? TaYLoRTANA (young), King. Op. cit. p. 9. 
Myrizus sauamosus, J. de C. Sow. Howse, Trans. T. N. F. C., vol. 1, p. 248, 1848. 
(?) — Hausmannti, Goldfuss. Geinitz, Versteinerungen, pl. 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 laminz of growth. Umbones 
ecurved at the point. Umbonal cavities, each with an oblique plate serving as a 
fulcrum 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 Schlotheim’s Mytilites acuminatus, for 
another shell, it has been deemed necessary to employ that of septifer for the present species. 
2 King, Catalogue, p. 10. 
3 Itis 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, Pl. XIV, ought to have been 
placed much further forward, where in fact it cannot be represented in the figure. 
