132 BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



Walls moderately strong; inner lamina slightly ribbed; the denticuli on the 

 bases of the parietal longitudinal septa are sharp. I could not see any trans- 

 verse septa in the parietal tubes. The radii are rather narrow, their summits 

 are remarkably jagged and very oblique ; the septa are plainly denticulated on 

 both sides, but chiefly on the lower side; each septum itself, toward the inner 

 lamina of the radius, branches and divides ; the interspaces are filled up nearly 

 solidly. The alse have apparently their summits less oblique than those of the 

 radii, their sutural edges are finely crenated. The lower edge of the sheath is 

 hollow underneath. The basis is flat ; it is rather thin, and imperfectly porose ; 

 in parts it is not at all porose, in others it is traversed only by very minute 

 pores ; there is, nevertheless, in some parts, even where the upper layer is not 

 porose, an underlying, cancellated layer. 



The labrum is deeply notched, with the edge almost plain, but show- 

 ing one very minute tooth in the specimen dissected (fig. 36<z). 



The mandible has four short spines and a lower cutting edge. 

 The hairs on the upper and lower edges are extremely short (fig. 36<^) . 



The maxilla has a deep notch below the upper pair of spines, which 

 are smaller than usual. There are about 22 spines below the upper 

 pair, and no enlarged one near the lower angle, such as the related 

 species have (fig. 36c) . 



The first pair of cirri has very unequal rami of 32 and 17 segments, 

 those of the shorter ramus strongly protuberant. 



Cirrus ii has subequal rami of 17 and 16 strongly protuberant seg- 

 ments. 



Cirrus iii has the anterior ramus a little longer, segments of both 

 rami moderately protuberant, and armed with long spines, as figured 

 for B. aquila. It has decidedly longer and more slender rami than 

 cirrus ii, both of 'about 20 segments. 



Cirrus iv has small groups of erect spinules on the distal anterior 

 parts of the lower segments, and a distal row of spinules, as in the 

 following cirri. 



Cirri v and vi have both segments of the pedicel densely spinulose 

 near their distal anterior borders, and the median segments have six 

 pairs of spines and a distal row of erect spinules (fig. 36&). 



Part of the spines of the cirri especially those inserted on their 

 inner faces are beautifully pectinated on one or both sides. 



Darwin's description, quoted above, applies to the small or moder- 

 ate-sized examples of California. The mouth parts and cirri are 

 described from a Monterey Bay specimen. In the northern waters 

 of Oregon to the southern boundary of Alaska, and especially in 

 Puget Sound and communicating waters, B. nubilis grows to a very 

 large size, and is remarkable for its thick, solid, yellowish, opercular 

 valves and the tendency to deepen the base, somewhat after the man- 

 ner of Megabalanus, whereas the species related to B. nubilis gain 

 room by lengthening the compartments. The shape of the tergum is 

 especially characteristic, the spur being wide at the base, tapering to 

 the narrow end, and standing rather remote from the basiscutal 



