THE SESSILE BARNACLES. 233 



density of the wall, which might sometimes result in apical denticula- 

 tion, though in all individuals I have seen the summits of rostrum 

 and carina are irregularly worn. 



In one specimen the rostrum and lateral comjiartments on one side 

 have been injured when the barnacle was half grown. Perfect repair 

 followed, but the rostrum was stunted, projecting very little below 

 the bases of the other compartments. The opercular valves are 

 normal. 



B. declivis is described here in some detail because it was known to 

 Darwin by but few examples not containing the soft parts, and ex- 

 cept for Verrill's brief note, its characters have not been noticed by 

 any other author. In view of the description of allied species from 

 west America and the East Indies, it does not seem superfluous to 

 confirm the characters assigned to B. declivis by the description of 

 other specimens. 



B. declivis is known from the Antillean f aunal province only, since 

 it is likely that Weltner's record from Bat j an ^ pertains to the closely 

 similar East Indian species B. longirostrum Hoek. 



BALANUS ORCUTTI Pilsbry. 

 Plate 55, figs. 2-2(7. 

 1907. Balanus orcutti Pilshry, Proc. Acad. Nat. Sci. Phila., p. 361, pi. 29, 

 figs. 1-7, September 28, 1907. 



Type. — ^o. 1783 A.N.S.P. Topot7jpes in the United States 

 National Museum. 



Distribution. — San Ysidro, Lower California, embedded in sponges, 

 collected by C. R. Orcutt. 



The walls are thin, impervious, the compartments not firmly ce- 

 mented together; basis membranous; rostrum boat-shaped, twice as 

 long as the rest of the wall, strongh'' arcuate and convex; the other 

 compartments nearly straight. Aperture small, oblong, toothed. 

 Parietes marked with growth-lines, and minutely, denselj'^ wrinkled, 

 the rugse transverse or oblique, in some places interrupted, forming 

 a pattern of long granules. 



Greatest diameter 11 mm., lateral diameter 9.2 mm., length of 

 rostrum 18 mm. 



The scutum is decidedl}^ less than half as wide as long. It is 

 sculptured with close, irregidar, deeply cut ridges of growth. 

 Articular ridge high and angular, about half as long as the tergal 

 margin, its lower end oblique. Articular furrow is very narrow. 

 The adductor ridge stands free of the much higher articular ridge. 

 It is strong and straight, running to the basal margin, close to and 

 slightly overhanging the pit for the lateral depressor muscle, which 

 is oblong and deep. Adductor scar well marked. 



1 Verzeichnis, p. 270. 



