228 BALAN1D.E. 



a single very broad longitudinal furrow, and those with 

 two rather broad, or with one narrow furrow, on their 

 scuta, could belong to the same species ; but I soon 

 found that all these varieties occurred mingled together, 

 and that they differed in no other respect whatever. 

 Generally, however, all the individuals in the same cluster 

 had the same variety of scutum, — thus adding one more to 

 the many instances amongst cirripedes of variations com- 

 mon to whole groups of specimens. Still more un- 

 willing was I to believe that var. nitidus and the common 

 variety could belong to the same species. Their general 

 aspect is totally unlike : var. nitidus has a smooth, clean, 

 naked shell, either white or pale purple, somewhat globulo- 

 conical, often with a nearly entire orifice ; whereas the other 

 common variety generally has a more steeply conical shell, 

 with a toothed orifice, and is covered by a dirty browmish 

 membrane. Moreover, though I have seen hundreds of 

 specimens from Tierra del Fuego, I have not seen one 

 specimen of var. nitidus, or even of an approach to it in 

 appearance ; and, on the other hand, var. nitidus is the 

 common form in Chile and Peru ; though I have seen one 

 or two specimens of the membrane-covered variety from 

 Valparaiso. Such facts strongly induced me to believe 

 that these forms were specifically distinct ; but upon careful 

 examination I could find no other or more important 

 differences than those just specified. Some specimens 

 from northern Chile are in an intermediate condition ; 

 and from Concepcion, in the south of Chile, where the 

 climate approaches in character to that of the more southern 

 parts of the Continent, there are many specimens, in so 

 intermediate a condition that I know not whether or no to 

 rank them under var. nitidus. Thus I became convinced 

 that these forms are only varieties. At Concepcion, some 

 few specimens are pale purple, and yet are wholly invested 

 by thick brown membrane, thus uniting the two extreme 

 varieties. From California I have seen both varieties, but 

 I do not know which is most common there. With respect 

 to the great difference in aspect between the specimens 

 from northern Chile and Tierra del Fuego, we shall here- 

 after see a strictly analogous case in Balanus Jloscu/us. 



