THE SESSILE BARNACLES. 



81 



The scutum has rather fine, ripplelike growth-ridges crossed by 

 clearly cut radial grooves. The articular ridge is very high and termi- 

 nates in a free point. Adductor ridge high but short; there is a small 

 ridge running parallel to it, near the depressor muscle insertion. The 

 upper part of the valve is thickened and rough. 



The tergum is broad, without an external furrow. The carinal 

 margin is highly arched, having a sort of low appendage built upon it. 

 Spur long, truncate at the end, and separated from the basiscutal 

 angle by about half its own width. There is a deep or shallow bay 

 in the basal margin on the carinal side of the spur, which, when fully 

 developed, gives the valve a thre&-pronged outline, very characteristic 

 of the species in its adult stage. The articular rib is moderately 

 developed, the crests for the depressor muscles usually weak. 



m 



FIG. 14. BALANUS EBURNEUS. a, PALPUS. 5, MANDIBLE, c, LABKUM. d, MAXILLA. SMITH'S CREEK, 



POTOMAC RIVER. 



The radii are wide, with oblique, somewhat crenulated and irregular 

 summits. (See p. 85, fig. 16&.) The parietes have strong, regular 

 internal ribs, the sides of which are usually minutely striated longi- 

 tudinally. The parietal tubes are copiously provided with transverse 

 septa, down to the base. There are usually 16 to 20 tubes in the 

 rostrum. Hollows behind the sheath are very shallow. The carina 

 stands steeper than the rostrum, and is sometimes recurved. The 

 basis is very porous, pores large near the periphery and having trans- 

 verse septa. 



Labrum armed with numerous teeth, with series of smaller teeth 

 running down the sides of the notch (fig. 14c). Palpi densely hairy in 



