176 



BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



notch, and bears five large spines, the next to the lower one largest 

 (as in the B. lalanus group). The rounded, receding lower ex- 

 tremity bears a group of 9 or 10 small straight spines, and the lower 

 edge has rather long bristles (fig. 55c). 



The first cirrus has rami of 14 and 10 segments, the posterior 

 ramus about two-thirds the length of the anterior. Cirrus ii with 

 slightly unequal rami of 12 and 11 segments. Cirrus iii with more 

 unequal rami of 12 segments. I see no spinules on the segments (yet 

 a few may be there, as the preparation is not very clear). Cirrus vi 

 has five pairs of spines on the median segments (fig. 555) . The penis 

 is longer than the sixth cirrus. 



D 



FIG. 55. BALANDS CRENATUS CURVISCDTUM. a, FIFTH KKOMKXT OF OUTER RAMOS OF 



CIRRUS III, SPECIMEN FROM STATION 3232. b, MEDIAN SEGMENT OF CIRRUS VI, TYPE. 

 C, MAXILLA. d, MANDIBLE OF THE TYPE. 



The shape of the plain, uncalloused scuta, the narrow spur of the 

 terga, the thin, weak walls, and the maxilla3 are all characteristic. 

 The characters vary in different colonies, about as much as in B. 

 crenatus, and in the limits of this work it is impossible fully to dis- 

 cuss or illustrate the local variations. Two of the forms may be 

 noticed. 



Specimens from Unalaska (pi. 41, figs. 1, 4) are typical in ex- 

 ternal form, but the tergum has a much longer carinal margin than 

 in the type lot. 



Numerous specimens (Cat. No. 32948, U.S.N.M.) from Albatross 

 station 3232, Bristol Bay, 10^ fathoms, have a remarkable resem- 

 blance to B. balanoides. The opercular valves and general form 

 are shown in plate 42, figures 2-2/7. They grew in crowded groups 

 which are very fragile, the compartments parting readily, so that it 

 is hard to handle them without breaking. The summits are deeply 

 toothed, the form tubular or club-shaped,' parietes having thin- 

 walled tubes, as in similarly shaped Atlantic forms of B. balanoides. 



