THE SESSILE BARNACLES. 



81 



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

 clearly ciit 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 iTinning parallel to it, near the depressor nniscle insertion. The 

 upper part of the valve is thickened and rough. 



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

 margin is higldy 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 tliree-fronged outline, very characteristic 

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

 developed, the crests for the depressor muscles usually weak. 



^^VV^v^l'|;l{/j-jff 



Fig. 14.— Balanus eburneus. a, palpus. 6, MAXoroLE. c, labrum. d, maxilla. Smith's creek, 



POTOMAC RIVER. 



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

 summits. (See p. 85, fig. 166.) The parietcs have strong, regular 

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

 tudinally. The parietal tubes are copiously provided with transveree 

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

 rostiTun. 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 scries of smaller teeth 

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



