THE SESSILE BARNACLES. 



105 



Compartments. The radii arc wide, with the summits making angles 

 of about 45 degrees with the base in young or small individuals, large 

 ones having nearly horizontal summits ; sutural edge with the laminae 

 denticulate below. Interior of parietes ribbed. Parietal tubes very 

 numerous, about 20 in the rostrum, without transverse septa, but filled 

 up near the apices. 



The basis clings very firmly to the walls. It is porous throughout, 

 and in large specimens the lower part is somewhat vesicular, though 

 it is nowhere very thick. 



The labrum of B. concavus has three teeth on each side of the notch, 

 according to Darwin; but in that from Long Beach (fig. 25c) there 



FIG. 25. BALANUS CONCAVUS PACIFICUS, LONG BEACH, CALIFORNIA, a, SECOND CIERUS 



OF LEFT SIDE. 6, MAXILLA. C, LABRUM. d, llTH SEGMENT OF THE ANTERIOR EAMUS OF 

 CIRRUS HI. , MANDIBLE. 



are none on one side and the outer one on the other side is bifid 

 or twinned. Such asymmetry in the labrum is so frequent as to be 

 hardly anomalous. In a specimen from Albatross station 2939 there 

 were two excessively minute teeth on one side, none on the other. 



The mandible has four teeth, the fifth united with the lower point. 

 The bifid tip of the second tooth in figure 25e is similar in both man- 

 dibles of the individual figured. In a specimen from station 2939 

 (fig. 266) the second tooth is minutely bifid on one side, simple on 

 the other, and the third and fourth teeth are very obtuse. This 

 tooth is often more or less noticeably bifid in other species of the 

 group. 



