220 BULLETIN m, UNITED STATES NATIONAL MUSEUM. 



the adductor ridge in some individuals, but these crests are entirely 

 wanting in others. 



The tergiim is long and narrow, with a furrow running to the 

 spur. Internally the articular ridge is continuous with the straight 

 ridge running to the spur. Spur rather long, bluntly pointed,' sep- 

 arated by about half its width from the basiscutal angle. 



These specimens differ from the types figured by Darwin by the 

 weakness or absence of the crests for the depressor muscles on the 

 scuta and by the distinctly wider terga. They are also rather 

 small, Darwin giving six-tenths of an inch as the maximum diameter 

 observed. 



By its solid wall, with irregular, roughened basal edge and inner 

 surface, this species is related to the Australian B. imperator^ but 

 both seem to be very distinct species. 



Siibgenns SOLIDOBALAWUS Hoek. 

 1913. t^oHdo-Balaniis Hoek, >S'/6o^ff-Expeditie, Monograpliie Sib, pp. 159,192. 



Small or minute barnacles with solid, rather thick wall compart- 

 ments, the parietes smooth or having few low ribs, the basis cal- 

 careous, radially gTOOved (or perhaps sometimes porous) ; usually 

 with wide, transversely grooved radii, which have septate sutural 

 edges. Opercular valves lodged high, projecting above the lateral 

 compartments. Scutum without longitudinal striation,.the adductor 

 ridge weak or wanting. Tergum with the spur rather narrow, 

 rounded at the end, its sides curving into the basal margin. Mandible 

 with the lower teeth acute, lower point spinose, a single series of 

 spines on the louder edge. Maxilla having few spines; a lower pair 

 enlarged. Outer surfaces of some segments of the third cirrus, or 

 the third and fourth, sometimes bearing small spinules. 



Type. — B. auricoma. 



DistrilnUion. — Indo-Pacific faunal province, chiefly in deep water. 



This group is rather hard to define succinctly, for want of con- 

 spicuous differential characters. The small size, the shape of the 

 terga, and the mandible, with spinose loAver point and a series of 

 long spines (in place of numerous hairs) on the lower border are its 

 chief diagnostic features in the series of nonporose Balani. It has 

 not the very wide tergal spur or conspicuously armed cirri of Ai'ma- 

 tohalanus. 



B. maldivensis and B. sociaUs (including B. ceneas) probabh^^ occur 

 nearly up to low-water mark, as well as in deeper waters. The others 

 are laiown from deep water only. 



The following species are not contained in the United States Na- 

 tional Museum : 



B. socicdis Hoek ( ? including B. ceneas Lanchester). 



B. maldivensis Borradaile. 



