CLass—CrusTacea. SuB-CLASS—-CIRRIPEDIA. 
Family—LePavivez. 
Cirripedia pedunculo flexili, musculis instructo: Scutis' musculo adductore solummodé 
instructis: valvis ceteris, sique adsunt, in annulum immobilem haud conjunctis. 
Cirripedia having a peduncle, flexible, and provided with muscles. Scuta! furnished 
only with an adductor muscle: other valves, when present, not united into an im- 
movable ring. 
Besides the brief characters here given others might have been added, drawn from the 
softer parts of the animals, but as this Volume treats only of Fossil species, they would 
have been in this place superfluous. Nor have I thought it advisable to give here any 
definition of the Sub-class Cirripedia, or of the Order which contains both the Lepadide 
and Balanidee, that is the Pedunculated and Sessile Cirripedes ; for the characters would 
likewise have had to be derived almost entirely from the softer parts of the animal. It 
may, however, be worth stating, that by following the metamorphoses of the Cirripedia, it 
can be clearly shown that the capitulum together with the peduncle, in the Pedunculated 
Cirripedes, and that the shell together with the operculum in the Sessile Cirripedes, that 
is the whole of what is externally visible, consists simply of the first three segments of the 
head. In many Crustacea the carapace, formed by the backward production of the three 
anterior rings of the head, covers the dorsal surface of the thorax, and in some it encloses 
the limbs and mouth. This is likewise the case with the Cirripedia, and it is only the 
wonderful elongation of the anterior part of the head, its fixed condition, and the absence 
of external eyes and antenne, which gives to the Cirripedia their peculiar character, and has 
hitherto prevented the homologies of these parts from having been recognised.” 
1 The meaning of this and all other terms is given in the Introduction at page 9. 
2 Nevertheless, in some Stomapoda, more especially in Leucifer of Vaughan Thompson, the anterior part 
of the head is only a little less elongated, compared with the rest of the body, than in the Cirripedia. 
That accomplished naturalist, M. J. D. Dana (Silliman’s ‘American Journal,’ March, 1846,) has stated 
that ‘the pedicel of Anatifa corresponds to a pair of antenne in the young :” although the peduncle or 
pedicel is undoubtedly thus terminated, this view cannot, I think, be admitted. In the larva, the part 
anterior to the mouth is as large, in proportion to the rest of the body, as in some mature Cirripedia: this 
anterior part supports only the eyes, antennz, and two small cavities furnished with large nerves, which I 
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