206 



BULLETIN" 93, UNITED STATES NATIONAL MUSEUM. 



the bases of the ribs minutely and very weakly denticulate. Basis 

 solid, denticulate at the edge, radially striate in the young (pi. 53, 

 %. 2). 



The scutum is noticeably warped in large specimens. It has strong, 

 somewhat unevenly spaced growth ridges and close, rather weak or 

 deep longitudinal strise. Inside there is a moderately prominent, 

 thin, articular ridge and a narrow articular groove. The adductor 



FIG. 65. BALANUS HAMERI. a, MAXILLA. Z>, MANDIBLE, c, LABRUM. 



ridge is wholly confluent with the articular rib above, running 

 straight to the basal margin, where it defines a rather large de- 

 pressor muscle pit. It is often weak or almost obsolete in American 

 specimens. 



The tergum has less coarse growth-ridges than the scutum, and 

 there are a few longitudinal strise near the carinal border. A furrow 

 leads to the spur, its sides more or less folded in in old specimens. 

 The spur is rounded at the end, moderately long, typically separated 

 by its own width from the basiscutal angle, but more distant in 

 most American specimens, in which it is sometimes separated from 

 the basiscutal angle by nearly double its own width. Articular 

 ridge short, sharp, and moderately high. Crests for the depressor 

 muscle sharp and numerous. 



The labrum has a very shallow notch and two teeth on each side 

 (fig. 65*). 



The mandible has four primary acute teeth, with smaller ones be- 

 tween the third and fourth and below the fourth (fig. 655). 



The maxilla has a notch below the upper large spines, and many 

 crowded spines on the edge below it. The upper edge is bearded for 

 a long distance (fig. 65#). 



Cirrus i has subequal rami of 16 and 14 segments. 



Cirrus ii with 17 and 19 segments, the rami subequal. 



Cirrus iii with 15 and 14 segments, the anterior ramus slightly 

 longer. The external anterior faces of the segments have many long 



