THE SESSILE BARNACLES. 



67 



Scutum dull purple, with smooth growth-ridges. Adductor ridge 

 strongly developed, rather acute. 



Terga white, shaped as in B. t. tintinnabulum, with a rather short, 

 acute beak; the external furrow closed; spur narrow; scutal margin 

 smooth. 



The labruni has a small median notch and no teeth on the shortly 

 hairy edge. 



Mandible with five well-developed teeth, the last united with the 

 lower point (fig. lla). 



Maxilla has 13 large spines, about as in B. t. tintinnabulum. 



Cirri about as in B. t. tintinnabulu7n } except that the segments of 

 the three posterior cirri are not so short, and the lower pair of spines 

 on each segment is smaller (lig. lib}. 



The above description applies to solitary specimens (figs. 2 to 2d) 

 not encrusted by nullipore, algao, or other marine growths. In the 



FIG. 11. a, MANDIBLE, AND b, MEDIAN SEGMENT OF CIRKUS vi, OF BAI/ANUS T. PENINSTJLAEIS. 



C, MEDIAN SEGMENT, CIRRUS VI, OF B. T. AZORICUS. 



large series comprised in Cat. No. 43487, U.S.N.M., the barnacles grow 

 in clusters (figs. 1, la), and are overgrown with algae, etc. The spines 

 in this lot are less fully developed, usually appearing only on some 

 of the compartments, the others being irregularly ribbed, plicate, or 

 nearly smooth. Some individuals lack spines altogether. The radii 

 are often smooth, rarely striate throughout. The color may be 

 soiled white throughout, or like the type, or lineate and clouded with 

 livid purple, the radii being livid purple, shading into white along 

 one side. The opercular valves are similar to the typical form. 



I worked over this race a long time in an attempt to identify it 

 with one or other of Darwin's named forms of B. tintinnabulum, 

 finally deciding to give it subspecific rank. Darwin's account of 

 B. t. dorbignyi Chenu, and Chenu's figure, resemble peninsularis rather 

 closely, yet differ by the oblique summits of the radii. Chenu gives 

 no figure of the opercular valves, and Darwin says that the tergum 



