486 BALANID.E. 



surrounded by several whorls of supplemental compartments 

 or scales : these are arranged symmetrically, and decrease in 

 size but increase in number towards the circumference and 

 basal margin. A well preserved specimen has a very elegant 

 appearance, like certain compound flowers, which when half 

 open are surrounded by imbricated and graduated scales. 

 The Chthamalinse, in the structure of the mouth and cirri, 

 and to a certain extent in that of the shell, fill up the 

 interval between the Balaninee and Lepadidae ; and Cato- 

 phragmus forms, in a very remarkable manner, the transi- 

 tional link, for it is impossible not to be struck with the 

 resemblance of its shell with the capitulum of Pollicipes. 

 In Pollicipes, at least in certain species, the scuta and terga 

 are articulated together — the carina, rostrum, and three 

 pairs of latera, making altogether eight inner valves, are 

 considerably larger than those in the outer whorls — the 

 arrangement of the latter, their manner of growth and 

 union, — all are as in Catophragmus. If we, in imagina- 

 tion, unite some of the characters found in the different 

 species of Pollicipes, and then make the peduncle so short 

 (and it sometimes is very short in P. mitella] that the valves 

 of the capitulum should touch the surface of attachment, it 

 would be impossible to point out a single external character 

 by which the two genera in these two distinct families could 

 be distinguished : but the more important differences in the 

 arrangement and nature of the muscles which are attached 

 either to the opercular valves or surround the inside of the 

 peduncle, would yet remain. 



Although all the valves of the shell, even the eight in 

 the innermost whorl, are very thin, yet from their number 

 in the successive whorls, and from each being concave in- 

 wards, so as to form a cavity or tube into which the corium 

 enters, the total thickness of the sides of the shell is very 

 considerable. Both of the species of Catophragmus oc- 

 curred mingled, in the one case with Tetraclita porosa and 

 in the other with T. jpurjmrascens ; now the walls of these 

 shells, we know, are very thick, and are permeated by 

 several rows of pores, occupied by threads of corium ; see- 

 ing this, we may be permitted to believe, that the several 

 exterior whorls of valves in Catophragmus, between which 



