498 VERRUCID.E. 



it may be considered as directly proved, that the two fixed 

 valves (s 7 and t' in all the figures in PL 21), which are 

 opposed to the moveable valves of the operculum (s and t), 

 consist of an extraordinarily modified scutum and tergum. 

 It has been shown (p. 129), that at the period of the meta- 

 morphosis, the two scuta, the two terga, and the carina of 

 the Lepadida), commence their growth, under the form of 

 the so-called " primordial valves," and so differ from all the 

 other valves when such occur : now, in two species of 

 Verruca, I have found closely analogous primordial valves 

 on the apices of both the moveable and fixed scutum and 

 tergum (thus affording strong additional evidence that their 

 nature has been rightly interpreted), and on one of the two 

 remaining valves, namely, that at the posterior or carinal 

 end of the shell. Hence, we may safely infer, that this 

 latter valve, which, though very much more developed on 

 one than on the other side, is so far medial as to curl round 

 and cover the line of opening between the moveable and 

 fixed tergum, is really a carina. The sixth valve differs 

 only very slightly in shape from the carina, and is directly 

 opposed to it ; therefore, in accordance with all analogy, it 

 must be the rostrum. Consequently, the shell in Verruca 

 consists of a moveable scutum and tergum, a fixed scutum 

 and tergum, a carina and rostrum, and, as we shall imme- 

 diately see, a membranous basis — the basis being, as in all 

 sessile cirripedes, the homologue of the peduncle in the 

 Lepadidae. 



The moveable scutum and tergum stand at about right 

 angles with the fixed pair ; and as these latter form a part 

 of the wall of the shell, which is always steep on this side, 

 the moveable pair, which close the orifice, are nearly hori- 

 zontal or parallel to the basis and surface of attachment. 

 Hence, the animal's body, which is attached between the 

 two scuta, but nearest to the moveable scutum, also, lies 

 nearly parallel to the surface of attachment; and I was 

 consequently at first led to suspect that the basal mem- 

 brane was one side of the shell in a modified condition ; 

 but the presence of the prehensile antennae of the pupa in 

 nearly the middle of this membrane, and the sheet of 

 cement-tissue on its under side, demonstrate that this mem- 



