52 



BULLETIN 1)3, UNITED STATES NATIONAL MUSEUM. 



Distribution. World-wide, in tropical and warm temperate seas; 

 into cold seas in the Southern Hemisphere. Low tide to about 30 

 fathoms. 



In B. tintinnabulum (various varieties) and B. algicola the cirri are 

 rather characteristic. The rarni of the third pair are exceptionally 

 short, like those of the second pair, the pedicel being rather long and 

 the first segment extremely broad. The general proportions of the 

 cirri may be seen in fig. 8. In other Balani therami of the third 

 cirri are decidedly longer than those of the second. Whether this pe- 

 culiarity characterizes the other species of Megabalanus I do not know. 



This is a group of littoral barnacles mainly of moderate or large 

 size. With the exception of B. tintinnabulum, all of them are 

 restricted to single faunal provinces, and are not especially variable. 

 B. tintinnabulum, in the Darwinian sense, has a range almost covering 

 that of the subgenus, but is represented by different races in the 

 several faunal districts. Several of the forms are commonly carried 

 on ships to ports all over the world. In north temperate latitudes 



Fia. 8. BALANUS TINTINNABULUM AZORICUS. CIRBI OK THE RIGHT SIDE, DRAWN FROM PHOTOGRAPH. 



the imported forms do not survive long, or at any rate they do not 

 become part of the local faunas. Whether any species of barnacle 

 has been colonized by ships, outside of its natural area, is unknown. 

 No data showing such colonization have been put on record, and 

 the collections before me afford nothing definite. 



Observations bearing on this point might easily be made in tropical 

 and subtropical ports. I have found fragments of B. tintinnabulum 

 along the water front of Honolulu, where it must be brought very 

 frequently, but no trace of it on the reefs east of the city, or on the 

 Anomia beds and rocks of Pearl Harbor, to the west, where other 

 barnacles are abundant. 



Many of the forms which are subordinated to B. tintinnabulum as 

 varieties or subspecies have a very distinct appearance. I can not 

 but believe that most of the races herein called subspecies (excepting 

 zebra, and galapaganus) will eventually be considered species. Darwin 

 has related his perplexity and repeated reversals of opinion in dealing 

 with them. This was partly due to the wide range of individual 

 variation, including the changes induced in the individual by the 



