THE SESSILE BARNACLES. 



223 



The outer maxillae are oval, rather densely covered with long 

 hairs. 



Maxilla (fig. 70a) has a small notch below the upper pair of large 

 spines, a short spine in the notch. Below it the straight margin 

 bears five principal spines, the lower two largest. The distal fourth 

 of the face and the lower margin have some delicate spines and the 

 upper margin several pairs of hairs. 



-Mandible (fig. 70c) with four teeth above the pointed, bispinose or 

 trispinose lower angle. Lower margin bears a close series of deli- 

 cate regular spines. The distal part of the inner face is hairy, and 

 there are five pairs of long hairs on the upper margin. 



Cirri — First pair with very unequal branches of G and 11 segments, 

 the shorter branch about two-thirds as long as the longer, with 

 strongly convex segments. 



Second pair, branches slightly unequal, of 8 segments which pro- 

 trude somewhat, and are densely hair3^ 



FlO. 70. BaLANUS HAWAIENRIS. a, maxilla. h, upper edge of LABRUAr. C, MANUIP.LE. 



Third pair, branches somewhat unequal, of 8 and 9 segments, 

 which protrude a little and bear fewer hairs than the second pair. 



Fourth to sixth cirri much longer, of long segments, with four or 

 five pairs of spines on each segment, the proximal one or two pairs 

 short (fig. 71a, fifth segment of cirrus vi). Cirrus vi has rami of 

 19 and 20 segments. The terminal segments have the distal pair of 

 spines ver}^ long (fig, 715). None of the cirri have any "teeth" or 

 spinules on the segments. 



The penis is extremely long, closely annulate, and \evy sparcely 

 hairy. 



Specimens from six localities indicate that tliis small barnacle 

 inhabits the entire HaAvaiian ridge, in the warm water (60° to 09° F.) 

 of moderate depths, down to 212 fathoms. It is usually seated length- 

 wise on the rough spines of the sea-urchin Phyllacantlms thoinaHi, 

 and is very uniform in the size attained, and in other characters, 

 throughout its range of about 1,700 miles. It is sometimes abundant. 

 On one spine 6 cm. long from Station 4064 there are about 108 

 individuals. 



