THE SESSILE BARNACLES. 



215 



The scutum is flat, and externally has close, cordlike growth-ridges 

 beautifully cut by deeply engraved longitudinal strire. Toward the 

 base there are very minute fringes of tine hairs. Inside there is a 

 rather low articular ridge fully three-fourths the length of the tergal 

 margin. Articular furrow very narrow and rather deep. The 

 adductor ridge is high and narrow, stands close to but deeply sepa- 

 rated from the articular ridge. Its acute continuation downward 

 does not reach to the basal margin. Adductor and depressor muscle 

 impressions rather deep. 



The tergum is flat, thin, delicately and regularly marked with 

 growth-striae. The spur is very short, half the width of the plate, 

 and truncate at the end. There is no longitudinal furrow or depres- 



FIG. 60. BALANUS KRTJGERI. a, STH SEGMENT OF CIRRCS in. 6, 12TH SEGMENT OF CIRRUS 



VI. C, MANDIBLE. (1, MEDIAN PART OF THE LABRUM. 



sioii externally, but slight grooves define the broad spur-fasciole. 

 Inside there is no articular ridge or furrow; the crests for the 

 depressor muscle are few and short; and under a strong lens the 

 middle and upper part appear minutely granose. 



Compartments are only weakly cemented together, but cling firmly 

 to the basis. The parietes of the carinolateral compartments are 

 extremely narrow (pi. 52, figs, le, If). The radii are narrow, with 

 very oblique, smooth, straight 'summits. Alse are not very wide, 

 their summits extremely oblique, smooth. Sutural edges smooth. 

 The interior surfaces of the parietes have regular, rounded longi- 

 tudinal ribs in the lower half, but are smooth above. The basal 

 laminse are continuations of the ribs, without intermediate laminae or 

 denticles, but they are firmly interlocked with the basis, and not to 

 be extricated without breaking. The sheath is conspicuously and 

 closely ridged transversely. 



The mandible (fig. 69c) has five rather slender teeth and a 'short 

 one above the lower point. 



