THE SESSILE BARNACLES. 203 



By the absence of radii and the shape of the opercular valves, this 

 is a rather isolated species. The cirri do not differ much from those 

 of Chirona, except that the rami of the forward pairs are decidedly 

 unequal, and there are no patches of minute spinules on the segments 

 of any of the cirri. 



The relationship I formerly thought I saw with species of Hexe- 

 lasma was in the superficial character of the absence of radii. Every- 

 thing else about this barnacle shows it to be a Balanus. 



Submenus CHIRONA Gray. 



1835. Chirona Gray, LYELL, Philosophical Transactions, of the Royal Society 

 of London, for 1835, pt. 1, p. 37, monotype Balanus tulipa Miiller= 

 B. ha me r I Ascauius. 



1913. Striato-Balanus HOEK, t&o#a-Expeditie, Monographic 31&, Cirripeclia, 

 p. 159, type B. amaryllis Darwin. 



Large or moderate sized Balani, with thin, poreless walls and cal- 

 careous basis; orifice conspicuously toothed; radii narrow or wide, 

 with thin, smooth, or sometimes weakly crenulated sutural edges. 

 Scuta without crests for the depressor muscles. Tergum with the spur 

 moderately long, not tapering. Cirri without " teeth " on the anterior 

 borders of the segments. Mandibles with the lower teeth well de- 

 veloped, basal margin hairy. 



Type. B. hameri. 



Chirona' 1 comprises two groups of species, the most important 

 structural differences being in the cirri. Of more significance, per- 

 haps, is the difference in habitat, the one group being boreal in 

 distribution, the other tropical. 



Part of the characters of this subgenus are evidently correllated 

 with the rather deep-water station of most of the species. The 

 weakly connected compartments, the absence of transverse, inter- 

 locking septa on the thin sutural edges (except in the littoral B. 

 amaryllis}, and the usual absence of color tell of a long existence in 

 quiet waters, with degeneration of the structures which give strength 

 to the ordinary shore barnacles. 



KEY TO SPECIES. 



ft 1 . Boreal group (Chirona s. str.). The substance of walls and valves is in- 

 variably white; compartments cohere feebly to each other and to the 

 basis; sutural edges of the radii and the opposed surfaces smooth, with- 

 out septa or denticles; basis solid. Rami of first pair of cirri subequal, 

 the segments not protuberant. Cirri iv to vi have many minute erect 

 spinules on the distal outer portion of part of the segments, and there 

 is a dense group of short spines on the anterior edge of the segments, 

 between the paired spines. Maxillte with many crowded, spines, without 

 an enlarged pair of spines on the lower part. 



i The derivation of the name Chirona is unknown. Gray coined many names of uncertain or undis- 

 coverable etymology, which must be accepted as they stand. Nobody has the right to assume that 

 Chirona is etymologically identical with Chiron or Chironia. 



