82 



BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



a broad band along the upper and distal borders, and having a series 

 of long spines at the distal fourth (fig. 14a). 



Mandible with three acute, widely spaced teeth, with thi-ee short, 

 blunt teeth below (fig. 14&). 



Maxilla has 17 spines, the smaller ones between the upper and 

 lower larger paii-s being pectinated. The lower pair stands on a long 

 prominence, below which the margin is densely hairy (fig. 14^). A 

 young specimen from Betterton, Maryland, 7 mm. diameter, has only 

 10 spines. 



Cirrus i has very unequal rami of 31 and 19 segments, those of the 

 shorter ramus very protuberant. 



Cirrus ii has unequal rami of 21 and 16 segments, all protuberant. 



Cirrus iii has 23 and 20 segments, the anterior ramus longer by six 

 segments. All the segments of the outer ramus are protuberant, the 



Fig. 15.— Balanus eburneus. a, 27th segment of cirrus vi. h, protuberant portion of the ISth 



SEGMENT OF ANTERIOR RAMUS, CIRRUS III. SMITH'S CREEK, POTOMAC KIVER. 



protuberance armed with a distal row of erect, spike-like spinules, a 

 rather large anterior area set with many short, conic spinules (fig. 

 15&). The posterior ramus has long spines in place of the anterior 

 patch of spinules, and a double subsutural row of erect spinules. 



Cirrus iv has the anterior ramus armed like that of cirrus iii; 

 posterior ramus without spinules. 



Cirri v and vi have no spinules. The segments bear 7 to 9 pairs of 

 spines, which as usual are pectinated near the end (fig. 15a). 



This is one of the common species along the Atlantic seaboard, to 

 be found wherever suitable situations offer standing room. Probably 

 the scarcity of records from the West Indies and Gidf of Mexico is 

 due to the small amount of shore collecting in those areas. The 

 smooth, neat contour, rather wide radii with jagged summits (but 

 often broken), the longitudinally striate scutum and pronged tergum 

 are such easy recognition marks that no one need mistake the adult 



