GENUS BALANUS. 177 



all of which have the parietes of their shells internally 

 quite smooth, or only irregularly roughened with points. 



Looking to the animal's bodv, in the Balaninae, the 

 labrum is always notched in the middle, and is never 

 swollen or bullate, for the outer and inner folds of mem- 

 brane of which it is composed lie close together. The 

 palpi are large, so that their tips almost touch each other. 

 The mandibles, generally, have their lower main teeth 

 laterally double. Of the cirri, the third pair invariably 

 much more closely resembles, in its whole structure, and 

 in its action, the second than the fourth pairs ; and it is 

 also generally separated by a small interval from the fourth 

 pair. 



I have already under the Family sufficiently entered on 

 the relations of the Balaninae to the Chthamalinse, and of 

 the genera, one to the other, so that I need not here add 

 anything. 



I can point out no difference in habits or geographical 

 distribution between the Balaninae and Chthamalinse. 



1. Genus — Balanus, Auct. 



* 



Conopea (pars generis). Say, Journal Nat. Sc. Philadelphia, vol. 



ii, part ii, 1822. 

 Messtjla (do.). Leach. Zoological Journal, vol. ii, 1825. 

 Chirona (do). J". B. Gray. Philosoph. Transacts., 1835, p. 37. 



Compartments six ; basis calcareous or membranous ; oper- 

 cular valves sub- triangular. 



Distribution. — Mundane : in the warmer seas. 



General appearance. — The shape of the shell in the 

 different species varies from depressed conical to cylindrical ; 



* The name Balanus was used, almost as at present, by Lister and Hill, 

 before the introduction of the binomial system. Since that period the first two 

 authors, as far as 1 know, who used this name, were Da Costa, in his ' Hist. 

 Nat. Test. Brit.,' in 1778 ; and Bock, in the ' Naturforscher,' for the same year; 

 Bock, however, applied it to a Chelonobia. 



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