THE SESSILE BARNACLES. 121 



1897. Balanus Isevis Bruguiere, Weltner, Verzeichnis, p. 263. 

 1909. Balanus Isevis nitidus Danviu, Pilsby, Proc. U. S. Nat. Mus., vol. 37, p. 68, 

 pi. 17; pi. 19, figs. 5-9. 



Type-Locality. — Cape Horn, on Mytilus TviageTlanicus, collected by 

 Dombey. 



Distribution. — Cape Horn north to the Rio Negro on the east coast, 

 and to Peru on the west. Shore to 20 fathoms.^ 



The barnacle is white or pale purple, covered with a bro-svn epi- 

 dermis (or nude in var. nitidus). Radii very narrow. 



Scutum having growth-ridges and one to three longitudinal fur- 

 rows, varying in width. Inside there is a rather narrow articular rib, 

 terminating helow in a free point, and a high adductor ridge wholly 

 free from the articular. Pit for the lateral depressor muscle is small 

 but deep. 



The tergum has a longitudinal furrow with the edges somewhat 

 folded in. Spur moderately long, wide, with the end obliquely cut off 

 and convex; basicarinal angle very thin; crests well developed. 



According to Darwin, ''in the cirri none of the segments are very 

 protuberant. In the first pair, one ramus is nearly twice as long as the 

 other. In the posterior pairs the segments are not much elongated, 

 but each supports seven pairs of spines." The more minute struc- 

 tures of the cirri have not been mvestigated. 



Darwin distinguished three varieties, or, as we would now say, sub- 

 species of B. Ixvis, characterized as follows: 



a*. Basis simply porose. 



b^. Walls covered with yellow or brownish epidermis; scutum usually with one 

 wide external furrow. Southern Chile, including the Straits ot Magellan. 



B. Isevis Bruguiere 

 62. Walls nude and smooth; scutum usually with two longitudinal furrows or 



one narrow furrow. Concepcion, Chile, to Peru B. I. nitidus Darwin 



a^. Basis much lengthened, its cavity partially filled with a mass of irregular, super- 

 posed septa of papery thioaeas, forming an openly cellular mass. 



B. I. coquiTmhertisis Sowerby 



The distinctive characters of Ixvis and nitidus are those of a great 

 majority of the specimens, but subject to exceptions, as Darwin has 

 noted. Some large groups from Gregory Bay, Magellan Strait, 

 though taken alive, had no epidermis. Over 50 individuals examined 

 had one wide furrow on the scuta (pi. 27, fig. 1), and one specimen had 

 an additional small furrow (pi. 27, fig. la). Numerous specimens 

 from other localities m the same region agree in having one wide 

 scutal furrow. Two individuals labeled Cape Horn, collector un- 

 known, have the normal yellow cuticle, but the scuta have two small 

 grooves, as in B. I. nitidus. A series from Valparaiso is similar, with 

 the epidermis of Ixvis, the scuta of nitidus. 



' The locality "California," given by Darwin, was based upon incorrectly localized specimens. The 

 species is confined to the cold water area of South America. Weltner reports specimens without sulci 

 on the scuta from Rio Grande do Sul, Brazil. 



