1G.2 BALANIDJB. 



torrid zones : there seems to me in all such cases to be 

 some degree of vagueness in the attempt to determine 

 which are highest or lowest, but I have already elsewhere 

 stated that Balanus is, probably, the most eminently 

 Cirripedial form, and exhibits in the strongest manner all 

 the characters by which Cirripedes differ from other Crus- 

 tacea ; as this genus is the largest, containing 36 species, 

 of which the habitats are known, I may state that of these, 

 exactly one third, or 12, inhabit both zones; 9 exclusively 

 inhabiting the torrid, and 15 exclusively the temperate 

 zones. According to the proportions of the whole class, the 

 numbers should have been 9 torrid, to only 11*11 tem- 

 perate ; so that evidently the genus Balanus (in one sense 

 typical) inclines towards the temperate regions more strongly 

 than does either the family or the sub-class to which it 

 belongs. 



With respect to the relation between the size acquired 

 by the different species of sessile cirripedes, and the tem- 

 perature of the localities inhabited by them, the genera 

 Chthamalus, Tetraclita, and Balanus, alone can serve for 

 comparison : in Chthamalus much the largest species is 

 found in the temperate zone : on the other hand, the two 

 largest species of Tetraclita are from the torrid zone, 

 though one of them also sometimes ranges into the tem- 

 perate seas : in Balanus, the largest species, and six other 

 species having a basal diameter sometimes over two inches, 

 inhabit the temperate regions ; and two out of these seven 

 species, flourish even in the Arctic seas ; whereas, within 

 the torrid zone, there are only three species with a diameter 

 sometimes exceeding two inches, but two of these frequently 

 become very large and massive ; so that Balanus, judging 

 from the size of the species, as well as from their range, 

 does not require for its highest development the temperature 

 of the torrid zones. 



The greater number of the species of the Balanidse have 

 wide ranges, as might be inferred from the fact of between 

 one third and one fourth of the total number inhabiting 

 both the torrid and temperate zones ; but it should not be 

 overlooked, that those species, as Balanus tintinnabulum, 

 ampkitrite, improvisus, and, in a lesser degree, B. trigonus 



