THE SESSILE BARNACLES. 



73 



cated or slightly overhanging. A ridge runs downward from it, 

 bordering the deep pit of the lateral depressor muscle, but there is no 

 adductor ridge. Pit for the adductor muscle is well marked. 



The tergum has the longitudinal furrow more or less open. Spur 

 rather short, with rounded end, situated about its own width, more 

 or less, from the basiscutal angle. Articular ridge strong. There 

 are no crests for the depressor muscle. 



Compartments. The parietes are typically smooth, but in some 

 conic, solitary individuals they have rather numerous ribs. The 

 radii are wide, with level summits. The lateral edges of the radii 

 and the opposed sutural edges are rather coarsely septate, but the 

 septa are either not distinctly denticulate, merely a little irregular, 

 or there may be a few coarse denticbs on on3 side (fig. 12c). The 

 hoiizontal pores of the radii are well developed. 



FIG. 13. BALANUS ALGICOLA. a, MAXILLA. 6, UTII SEGMENT OP CIRRUS vi. c, MANDIBLE, d, MORE ENLARGED 



THIRD TOOTH AND LOWER POINT OF THE MANDIBLE. 



The basis is not very thick. It is radially porous, without a cel- 

 lular under-layer, so far as seen. 



The labrum has three minute teeth on each side. The mandible 

 has three strong teeth, the fourth and fifth being quite small and 

 short (fig. 13c, fZ). 



The maxilla has 8 to 10 large spines. The margin protrudes some- 

 what toward the lower border (fig. 13o). 



The cirri are purple. The first three pairs are quite short, as in 

 tintinnabulum; the later ones are not very long, and have segments 

 a little wider than long. The sixth pair has rarni of about 22 segments 

 with from six to eight pairs of spines on the middle segments (fig. 

 136). I could find no spinules along the distal borders of the segments, 

 such as other races of B. tintinnabulum have. 



