138 



BULLETIN 93, UNITED STATES NATIONAL MUSEUM. 



By the shape of the tergum, which has a tapering spur, wide at the 

 base, and remote from the basiscutal angle, this species is related to 

 B. nubilisj but the far less deeply sculptured exterior of the opercular 

 valves, and the very weak development of ridges on the inner faces 

 of the valves, readily distinguish B. fios from its larger, coarser com- 

 panion at all stages of growth. The color of walls and valves, the 

 smaller size, the very deeply toothed orifice, and the armature of the 

 cirri are further differential features. 



In B. spongicola Brown, the spur of the tergum is wider, shorter, 

 and nearer the basiscutal angle; the scutum has much more deeply 

 cut growth ridges, which are distinctly beaded, and the articular and 

 adductor ridges are stronger. The summits of the radii are more 

 oblique in B. flos, and the apices of the opercular valves diverge. 

 There are important differences in the cirri. 



B. flos seems to have an unusually great range in depth, but possibly 

 the example from Albatross Station 4420 had been washed into deep 

 water from somewhere near the surface. 



SERIES OF B. BALANUS. 



Balani with the ribs on the inner face of the parietes more num- 

 erous than the septa in the wall ; basis not porous ; maxilla with one 

 spine near the lower angle much larger than its neighbors. 



This boreal group extends into the cool Temperate Zone. It is 

 prolific in races and local forms, especially in Bering Sea and the 

 North Pacific probably its center of radiation. There are only two 

 clearly defined species, distinguished as follows: 



Parietal pores without transverse septa, though usually filled up above 



B. balanus, p. 149. 

 Parietal pores having transverse septa, at least in the upper half D. restrains. 



BALANUS ROSTRATUS Hoek. 



Plate 36, figs. 1, 2, 2a, 



1854. ?B. porcatus * * * some fine, brilliantly white specimens (with- 

 out opercula) from the coast of China, DARWIN, Monograph, p. 259. 



1883. Balanns restrains HOEK, Challenger Report, Zoology, vol. 8, p. 152, 

 pi. 13, figs. 16-22. 



1900. Biilfnms porcatus Da Costa, WELTNER, Fauna Arctica, vol. 1, p. 296, 

 pi. 8, fig. 13. 



