THE SESSILE BARNACLES. 



175 



NORTH PACIFIC, BERING SEA, AND ARCTIC OCEAN. 



BALANUS CRENATUS CURVISCUTUM, new subspecies. 



Plate 41, figs. 1, 4 ; plate 42, figs. 1-16, 2-2<Z. 



Type. Cat. No. 48037, U.S.N.M., from Bristol Bay, Alaska, col- 

 lected by C. L. McKey. Growing on Mytilus. 



Form usually cylindric, the walls thin, weak, or fragile, white, 

 formed of very thin outer and inner lamince joined by delicate septa 

 forming square or irregular pores, of which there are 10 to 12 in 

 the rostrum. Parietes smooth or nearly so. Radii rather narrow 

 usually, but sometimes wide in the rostrum. Basis very thin, pore- 

 less. 



Size rather small, the largest 14 mm. in diameter, with a height 

 of 1.1 mm. The figured type measures, diameter 10 mm., height 

 11.4 mm. Another of the same group measures, diameter 9.5 mm., 

 height 12.3 mm. 



The scutum is usually warped strongly, externally concave between 

 base and apex. It has an unusually long basal margin, equal to or 

 exceeding the tergal margin, is thin, and smooth inside, without 

 callouses or distinct muscle impressions. The articular ridge is thin 

 and well reflexed. 



The tergum has the spur narrower than in crenatus, the articular 

 ridge forms a triangular projection overhanging the furrow and 

 scutal margin. The scutal border is rather broadly inflected at a 

 right angle with the face of the valve. 



The maxilla has a notch below the upper pair of great spines, 

 several small spines standing in it. The edge advances below the 



