doubt have the power of scraping, like a lip, anything
towards these prehensile organs. It will hereafter be seen, that the
male of _Ibla Cumingii_, in which the cirri are quite rudimentary,
obtains its food in a somewhat analogous manner, though in this case the
whole peduncle moves, and not merely a probosciformed mouth: it deserves
attention, that in the male Ibla and in Anelasma, in neither of which
the cirri are prehensile, the palpi are rudimentary and useless. I am
tempted to believe, that the largely developed olfactory sacks, and
perhaps, likewise, acoustic (?) sacks, in Anelasma, replace, by giving
notice of the proximity of prey, the loss of tactile cirri. It should be
remembered that all Cirripedes subsist on animals which happen to swim
or float within reach of the cirri; but here it is only those which
happen to crawl within reach of the probosciformed mouth. It would,
however, be rash to assert that the cirri in Anelasma, considering their
muscular though feeble structure, may not be of some slight use, when
thrown over the prey, in preventing its escape.

Professor Steenstrup informs me that, from late observations, it appears
that this animal always adheres to the shark's body in pairs. I regret
extremely that I have not been able to examine a pair: that the
individual examined by me was bisexual, I can hardly doubt, though the
male organs certainly were feebly developed; it appears probable, that
the individual described by Loven was likewise bisexual: but after the
facts presently to be revealed regarding the sexes in Ibla and
Scalpellum, it is quite possible that the male and female organs may be
developed in inverse degrees in different and adjoining individuals.

The genus Anelasma is, I think, properly placed between Alepas and Ibla.
In several of its characters, such as the absence of calcareous valves,
the broad blunt end of the peduncle, the spineless cirri, the small size
of the trophi, and more especially the absence of transverse striae in
those muscles, which in mature cirripedes are thus furnished, we see
that this genus is in some degree in an embryonic condition.

_Genus_--IBLA. Pls. IV, V.

IBLA. _Leach._ Zoolog. Journal. vol. ii, July, 1825.

ANATIFA. _Cuvier._ Mem, pour servir, ... Mollusques, Art. Anatifa,
1817.

TETRALASMIS. _Cuvier._ Regne Animal, 1830.

(_Foem. et Herm._) _Valvae 4, corneae: pedunculus spinis corneis,
persistentibus vestitus._

(Fem. and H