160 



BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



ous simple spinules on the anterior ramus, very few on the pos- 

 terior. Long spines are copiously developed on both rami. Cirrus 

 iv has a small group of mostly simple spinules on the anterior 

 distal part of the segments. The sixth cirrus has rather short 

 segments bearing six to seven pairs of spines. Penis about half 

 as long as sixth cirrus, with the usual point near the base. The 

 great inequality of the rami of cirrus i and the large number of 

 spines on the later cirri differentiate this form from Atlantic speci- 

 mens (fig. 46). 



13 



FIG. 47. BALANUS BALANUS, ST. PAULS ISLAND, a, l>, BOTH sinus OF A PALPUS, c, 22o 



SEGMENT OF CIRRUS VI. d, LAERUM. 



In a specimen from St. Pauls Island, Bering Sea, the labrum 

 has two small teeth on each side, mouth parts otherwise typical. 

 First cirrus with rami of 24 and 12 segments. The third and 

 fourth cirri have very few small spinules, not so many as in the 

 Bar Harbor form. The sixth cirrus has six to seven pairs of 

 spines, as in the preceding form, from which this differs by having 

 teeth on the labrum. The penis has the usual point near the 

 base, and is less than half as long as the sixth cirrus (fig. 47). 



By the numerous spines of the cirri the Bering Sea B. balanus 

 resemble B. re-stratus, yet the characters of the opercular valves, the 

 absence of septa in the parietal tubes, and the more ribbed external 

 wall are characters which surely indicate that they belong to the 

 Atlantic species. 



