192 BALANIDiE. 



Geographical Distribution. — This, which is much the 

 largest genus of sessile cirripedes, has its species scattered 

 over the whole world, from the arctic regions, in lat. 74° 48', 

 where we have B. crenatus and porcatus, throughout the 

 tropical seas, to Cape Horn, where B. Jlosculus adheres to 

 the coast-rocks. Many of the species have individually very 

 wide ranges ; thus B. tintinnabuluni and amphitrite are 

 found throughout the warmer seas ; but the wide distribu- 

 tion of these species may be partly due to their frequent 

 adhesion to ships' bottoms : B. crenatus ranges from the 

 frozen seas, in lat. 74° 48' north, to the West Indies and 

 Cape of Good Hope — a wonderful endurance of the most 

 opposite climates. Balanus improvisus, again, extends from 

 Europe to Nova Scotia, thence southward to Patagonia, and 

 up the western coast of S. America, someway north of the 

 Equator. Most of the species have considerable ranges ; 

 thus of the six species found on the eastern shores of 

 northern America, five of them occur in Great Britain. Of 

 the thirty-six species of which the habitats are known, ex- 

 actly one third, or tw T elve, inhabit both the torrid and tem- 

 perate zones, these being divided by the isocryme of 68°; 

 nine are found exclusively in the torrid, and fifteen exclu- 

 sively in the temperate zones. Within the warmer latitudes, 

 and especially in the southern hemisphere, Tetraclita and 

 Elminius to a certain extent supplant Balanus. In depth, 

 the species range from the upper limits of the tidal zone to 

 even fifty fathoms. Balanus improvisus and eburneus are 

 able to survive in brackish water. The different species are 

 attached to various surfaces — rocks, shells, timber, floating 

 objects, sea-weed, lamelliform corals, Milleporae, Gorgonise, 

 and even to sponges. Mr. G. B. Sowerby has remarked* 

 that in the species from the southern hemisphere it is the 

 basis, and in the species from the northern hemisphere it is 

 the parietes, which are elongated, when the individuals, from 

 being crowded together, become cylindrical ; but this is erro- 

 neous ; B.perforatus, in the northern hemisphere, sometimes 

 has an elongated basis ; but no doubt the basis of our com- 

 monest species, as B. balanoides, crenatus ■, and porcatus t 



* Darwin's ' Geology of S. America/ p, 264. 



