146 



BULLETIN 93^ UNITED STATES NATIONAL MUSEUM 



and sixteenth segments of cirrus v) . There are also some spines along 

 the distal sutures of the segments of the outer ramus of cirrus vi 

 (fig.41&).^ 



The penis is very long, over 20 mm., purplish, densely and conspic- 

 uously annulated, with a very few short hairs near the end. There 

 is a blunt projection on the dorsal base. 



A paratype of apertus examined has numerous simple bifid and 

 trifid spinules on the segments of cirrus iii, also a band formed of 

 several rows of minute, flat, fimbriated spines on the distal borders 

 of the segments. Cirrus iv has a row of sutural spinules, but none 



Fig. 42. — Balanus rostratus apertus (Cat. No. 38667). a, 1st cirrus, h, mandible. 

 V, maxilla, d, 15th and 16th segments of cirrus \. 



were seen on vi. The palpi are similar in structure to those of 

 B. balanus, except that the bristles are all very much smaller and 

 shorter. 



Typical B. r. apertus is readily distinguishable from typical 

 B. rostratus by the thinner wall, cylindric form, with large orifice, 

 the wider, not sunken radii, and esi^ecially by having more tubes in 

 the parietes, about 18 in the rosti-um, without transverse septa in 

 the lower part, against about 14 in B. rostratus, where the septa 

 extend close to the base. The tergum is narrower for its length, 

 and, while usually white, it sometimes has a beautiful pink (vina- 

 ceous) tint, which also colors the apices of the scuta in some of 

 the specimens taken by Dall at Unalaska. The only tangible dif- 

 ferences between the appendages of this form and B. halanus is 

 that the number of spines on the segments of the cirri is greater in 

 B. r. apertus^ and the penis is decidedly longer. 



