THE SESSILE BATJNACIJRR. 



143 



Tergum is nearly as in B. r. apertus. The spur is rather short and 

 narrower than in B. balanus pugetensis. The in flexed scutal margin 

 also is narrower (pi. 30, fig-. 7). 



Mouth parts. The labrum is very shortly hairy, with a single 

 almost obsolete tooth on each side (fig. -JO&). Mandibles as in B. r. 

 apertus. Maxilla with the three major spines nearly twice as long as 

 the minor spines, of which there are 13. 



Cirri. Cirrus i has rami of 13 and 24 segments; cirrus ii has very 

 slightly unequal rami of 15 segments each ; cirrus iii has more unequal 

 rami of 18 and 15 segments, those of the anterior ranius armed with 

 a few spinules. Cirrus vi has about 40 segments. There are at most 

 four pairs of spines, the lower pair very small (fig. 40(7) . 



The penis is long, but shorter than in B. r. apertus, about as in B. r. 

 cdaskensis. 



With the external form of B. rostratus apertus, this race has trans- 

 verse septa in the lower as well as the upper part of the parietal tubes, 



FIG. 40. BALANUS ROSTEATUS HETEROFUS, TYPE, a, 27Tit SEGMENT OP CIURUS vi. 1), LA- 

 BRUM AND PALPUS. C, B. E. ALASKENSIS, MAXILLA. 



and the posterior cirri have few spines, like B. balanus pugetens'ls. 

 The numerous and small parietal tubes, well furnished with trans- 

 verse septa, are characters like B. rostratus apertus, or perhaps more 

 like B. r. alaskensis, since there are septa in the lower parts of the 

 tubes. It should be noted that in the reduced number of spines on 

 the posterior cirri, B. r. heteropus and B. r. alaskensis resemble one 

 another. 



Figures 5, la, 8, 9 and 10 of plate 36 have the outer lamina of the 

 parietes partly filed away, to show the parietal tubes and septa. 



B. r. heteropus and B. It. puget&ns-ls occur together in both localities 

 given above, sometimes growing upon the same shell or upon one 

 another. They are exceedingly similar externally, and can not be 

 separated without thorough examination. In the large series I have 

 studied there are no individuals suggesting intergradation or hybrid- 

 ism. 



The specimens from the San Juan Islands approach the size of 

 B. r. apertus, the largest measuring 23 mm. in carinorostral diameter, 



