THE SESSILE BARNACLES. 185 



by the callus below the articular ridge. The callus between the 

 adductor pit and the articular ridge is sometimes grooved, somewhat 

 as in B. hesperius, but much less strongly. The tips of the opercular 

 valves do not diverge as they frequently do in B. crenatus. When 

 the surface has been at all disintegrated, the tips of the scuta form 

 a square projection locked into the terga. The first and third cirri 

 differ from those of B. crenatus. 



In the walls, but not the opercular valves, B. balanoides often has 

 very much the appearance of Chthamalus stelJatus. The name 

 Chthamalus europceus Philippi seems to have been applied to Helgo- 

 land specimens by some authors. 



In patellif orm and tubular specimens from New Haven and a high 

 conic specimen from Nahant, I found six pairs of spines on the seg- 

 ments of the later cirri, and rarely a seventh minute pair. In a 

 patelliform individual cirrus i has 13 and 9 segments, cirrus ii 10, 

 cirrus iii 12 and 10, and cirrus vi 30 segments. There are no spinvlcs 

 or " teeth " on elm Hi and iv, such as are found in B. crenatus. The 

 bristles at the posterior distal angles of the segments are always very 

 short. In a tubular specimen the labrum has four teeth on each side. 

 In a conical one from the same place there are four teeth on one side, 

 five on the other. In all, the mandibles and maxilla? could not be dis- 

 tinguished from some B. crenatus; but there is never a- notch below 

 the upper pair of spines of the maxillre in B. balanoides (fig. 58). 



The elongated, tubular, or trumpet-shaped form (fistulosus Bru- 

 guiere) is in no sense a race, as it is commonly found in the same group 

 with patelliform individuals, as in the group figured from Savin 

 Rock, New Haven, Connecticut. Usually the shape may be attributed 

 to crowding, but, as both Gould and Darwin have noted, extremely 

 lengthened, club-shaped individuals are often found growing soli- 

 tary, under such circumstances that neither crowding nor the nature 

 of the supporting object can be responsible for the shape of the 

 barnacle. Plate 44, figure 4, represents such a solitary specimen from 

 Loch Fyne, Scotland, Gl mm. long, 11 mm. in greatest diameter, the 

 tube smallest (5.5 mm. diameter) near the base. 



Small cylindric crowded specimens from sandstone rocks near 

 Exmouth, England, measure 8 to 18 mm. long, the tube near the base 

 2 to 5 mm. in diameter. 



Figures 1-1&, plate 44, represent the rostrum, interior and exterior 

 of a conic specimen from a buoy at Exmouth, channel coast of Devon, 

 diameter 22 mm., height 8.5 mm. 



A series from Arctic Island, Cumberland Gulf, consists of patelli- 

 form individuals only. Another from Cumberland Gulf contains 

 transitions from the patelliform to cylindric, the latter solitary and 

 mainly of large caliber, height 21 mm., diameter 12 mm. (pi. 44, figs. 

 3, 



