Class — Crustacea. Sub-class — Cirripedia. 



Family — Lepadid^. 



Cirripedia pedunculo flexili, musculis instructo : Scutis^ musculo adductore solummodo 

 imtrudis : valvis cceteris, siquce adsunt, in annulum immobilem haud conjunctis. 



Cirripedia having a peduncle, flexible, and provided v^^itli 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 Lepadidae 

 and Balanidse, 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 

 wonderfid elongation of the anterior part of the head, its fixed condition, and the absence 

 of external eyes and antennae, which gives to the Cirripedia then' pecuhar character, and has 

 hitherto prevented the homologies of these parts from having been recognised." 



^ The meaning of this and all other terms is given in the Introduction at page 9. 



2 IVevertheless, 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 accomphshed naturahst, M. J. D. Dana (Silliman's 'American Journal,' March, 1846,) has stated 

 that " the pedicel of Anatifa corresponds to a pair of antenna; 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, antennae, and two small cavities furnished with large nerves, which I 



