200 



BULLETIN OF THE BUREAU OF FISHERIES. 



beveled margin of the lower half of the occludent border there is an inflected sharp rid.ee. Toward 

 the basal margin the inner surface is longitudinally grooved. 



The tergum (pi. vin, fig. 5, Gi has a long purple beak, one-fourth the length of the whole plate. 

 The outer surface is worn above, but the lower part is cancellated like the scutum. The longitudinal 

 .sulcus is closed by infolding of its sides. The spur is long, rounded at the end, and situated at less 

 than its own width from the scutal margin. On both sides the basal margins slope steeply to the spur. 

 The interior is yellow, with a long purple spot in the middle. Articular ridge short, suberect and 

 thin. A low, flat, gently arcuate rib runs from the spur to the apical beak, in which a fine cavity 

 penetrates from the apex of the purple spot. The depressor crests are few and not very strong. 



Basal length of the walls 70 mm., height 75 mm. Length of the scutum 31 mm., breadth 13.5 mm. 

 Length of tergum with spur 32 mm., breadth 12 mm. 



The mandible (fig. 2. b, left side) has four small teeth, the last adjacent to several low obtuse denticles 

 at the lower end. The end of the maxilla is sigmoid, the upper half excavated, the lower convex. 

 It is armed with numerous stout and slender spines (fig. 2, c, right Bide). The first pair of cirri has 

 wide rami like moth antennae, the posterior one three-fourths as long as the anterior, with greatly 

 protruding segments, about 22 in number. The segments of the anterior ramus are less protruding 



Fig. 2.—Balanus aquita. a. Second cirrus; p. mandible; c, maxilla. 



and about 30 in number. The second cirri (tig. 2. a have subequal branches, and the protrusion of 

 the segments reaches its maximum. The third cirri are longer, with much less protruding segments. 

 The other cirri are much more slender, longer, with about 5 pairs of long spines on each joint. 



Type, no. 32403, U. S. National Museum, from Albatross station -4490, off Santa Cruz Light-House. 

 10 fathoms, fine gray sand and rock bottom. 



The dense structure of the walls of this species would almost entitle it to a place in Darwin's 

 section C of the genus Balanus; but it is clearly related to B. psittacus of the Chilean coast by the 

 structure of the opercular plates and the cirri. It differs from B. psiltucus in the following respects: 



The sculpture of the opercular plates is unlike, tin- longitudinal grooves being far deeper, and the 

 transverse ridges closer. The occludent margin of the scutum is bent inward, as well as the tergal 

 margin. The adductor ridge in the scutum stands free from the articular ridge throughout, whereas in 

 /;, psittacus the confluence < if the two ridges forms a deep vaulted cavity above the depressor muscle 

 impression. The terga are much alike, but in /;. aquila there is no ridge along the carinal side of the 

 purple streak, Buch as incurs in /;. psittacus, and externally the longitudinal sculpture is coarser and 

 the transverse much closer. There are numerous other differences in the walls, etc., but those given 

 above are amply sufficient for the discrimination of the species. 



