156 BALANID^. 



rare species of Cirripede be brought from some one quarter 

 of the world, characters beautifully defined may not be 

 readily discovered. In determining what forms to call 

 varieties, I have followed one common rule ; namely, the 

 discovery of such closely-allied, intermediate forms, that 

 the application of a specific name to any one step in the 

 series, was obviously impossible; or, when such inter- 

 mediate forms have not actually been found, the knowledge 

 that the differences of structure in question were such as, 

 in several allied forms, certainly arose from variation, — for 

 instance, in the case of two shells otherwise identical, one 

 being longitudinally ribbed and the other smooth, a charac- 

 ter which we know to vary, — but I have always used this 

 argument from analogy with great caution. Finally, 

 as in the large genus Balanus, there is an especial amount 

 of variation, I have there entered in detail on this subject ; 

 and I hope that those interested in it, will refer to that 

 discussion, which is almost verbally applicable to some other 

 genera of the family, as Tetraclita and Chthamalus. 



Bate of Growth. Exuviation. Powers of Bepairing In- 

 juries. — In my former volume I have shown that the 

 pedunculated cirripedes grow rapidly ; this is likewise the 

 case with the Balanidse. Mr. Stutchbury informs me that 

 he has seen numerous specimens of Balanus tintinnabulum 

 from 2 to 3 inches in height and from 5 to C inches in 

 circumference (and this is nearly the full size which the 

 species attains), on a vessel which had been to sea only 

 during one year. At Coquimbo, in Chile, I have seen a 

 specimen of B '. psittacus 1*3 of an inch in basal diameter, 

 and '8 in height, adhering to a chain that had been only 

 six months under water. Poli, also, gives the case of some 

 Balani (probably B. perforates) , which, in about four 

 months, had attained a basal diameter of 1 inch, and a 

 height of ljth of an inch. Balanus balanoides is a smaller 

 species, and of slower growth ; for the late Mr. W. 

 Thompson, of Belfast, found that in three months from 

 July 3d, certain marked specimens had increased from 

 2J — 3 lines to 4£ lines, which is the usual maximum size 

 attained in that locality. From other observations, Mr. 

 Thompson believes that the extreme duration of life of this 



