alasmis
dilatata_ of Leach; and for a long time I considered it as a distinct
species. It differs from _L. anserifera_, in the less thickness of the
valves, in their being more finely and yet plainly furrowed; in the
greater width of the scuta; and more especially, of that part of the
valve lying between the occludent margin, and the ridge running from the
umbo to the apex; in the less elongation of the area in the terga,
bounded by the two occludent margins; and, lastly, in the less size of
the whole individual. The trophi and cirri are absolutely identical.
Lately, however, in carefully going over a great suite of specimens, all
the above few distinctive characters broke down and insensibly graduated
away; and I am convinced that this form is only a variety of _L.
anserifera_; its different aspect being caused partly by youth, but
chiefly, I suspect, from being attached to light objects floating close
to the surface of the sea.

The _Lepas anserifera_ can be distinguished by the slight furrows on its
valves from all the other species, excepting _L. pectinata_: this latter
species can be readily known, by the close proximity in the scuta of the
occludent margin, and the ridge extending from the umbo to the apex; by
its carina being very narrow above the fork; by the prongs of the fork
diverging at an angle of from 135 deg. to 180 deg.; by the thinness of its
valves; by the coarseness of the furrows on them; and lastly, by there
being at most in _L. pectinata_ only one filamentary appendage beneath
the first cirrus.

4. LEPAS PECTINATA. Pl. I, fig. 3.

LEPAS PECTINATA. _Spengler._ Skrifter Naturhist. Selbskabet, 2,
B. 2, H., 1793, Tab. X, fig. 2.

---- MURICATA (var.) _Poli._ Test. Utriusque Scicil., vol. i, Pl.
vi, figs. 23, 29, 1795.

LEPAS ANSERIFERA. _Poli._ Test. Utriusque Scicil., vol. i, Pl. vi,
figs. 25-27.

---- SULCATA. _Montagu._ Test. Brit., Pl. i, fig. 6, 1803.

PENTALASMIS SULCATA. _Leach._ Encyclop. Brit. Suppl., tom. iii,
Pl. lvii, 1824.

---- spirulae (!) (var.) _Leach._ Tuckey's Congo Expedit. Appendix,
1818.

---- RADULA (var.) et SULCATUS. _Brown._ Illust. of Conchology,
Pl. li, figs. 3-6, 1844.

---- INVERSUS. _Chenu._ Illust. Conchy., Pl. i, fig. 14.

ANATIFA SULCATA. _Quoy et Gaimard._ Voyage de l'Astrolabe, Pl.
xciii, figs. 18, 20.[28]

[28] I may add, that I have received many specimens incorrectly