THE SESSILE BARNACLES. 283 



The morphology of Xenobcdutms has been very fully discussed by 

 Darwin, who has demonstrated its relationship to other Coronulinse, 

 and especially to Tubicinella. He writes: 



In the shell the aflinity is almost equally close to Coronula and Platylepas, 

 but considering the whole animal, the affinity is somewhat closer to Tubicinella. 

 Xcnobalanus may indeed be described as a Tubicinella without opercular 

 valves with the opercular membrane thickened down to the basis and with 

 the shell, excepting the few last-formed basal zones of growth, almost wholly 

 removed by the breakage of its upper end ; this remnant of a shell, however, 

 presenting some strong points of resemblance to Coronula. 



The tendency toward degeneration of the opercular valves, notice- 

 able in Coronula, culminates in Xenobalaanus^ where they are entirely 

 Avanting; but the hoodlike borders of the oral orifice are developed 

 more than in the other genera. 



XENOBALANUS GLOBICIPITIS Steenstrup. 

 Plate G5, figs. 2, 2a, 2b. 



Distribution. Northern Atlantic, near the Azores between Ma- 

 deira and England, and the Faroe Islands; New England, on the fins 

 of the blackfish, GlobiocepJialus. 



It is described by Darwin as follows : 



General appearance. The shell is in an almost rudimentary condition, and 

 appears like a small white irregular star, embedded up to its top in the skin 

 of the porpoise. Out of this thin, star-shaped shell a cylindrical flexible, 

 peduncle-formed body springs, which forms the main part of the animal ; it is 

 narrow where corning out of the central cavity of the star, but soon acquires 

 its full diameter ; at the upper end it has a reflexed hood, and hence is broader, 

 and this has the appearance of forming a capitulum, like that of a pedunculated 

 Cirripede. This pseudo-capitulum is formed by a membranous reflexed collar 

 or hood, whi.-h is very narrow at the lower end of the orifice, close under the 

 mouth, and becomes wider and wider toward the upper and carinal or posterior 

 end of the orifice ; hence the lower reflexed edge of the hood is only slightly 

 oblique or even nearly transverse. The orifice leading into the sack is large 

 and nearly in the same straight line with the peduncle ; it is a little hollowed 

 out in the middle at the upper end, and on each side of this medial hollow there 

 is a small, rounded projection or horn, not perforated, but hollow, as may be 

 seen by turning up the hood and looking at its under side. These two little 

 horns curiously bring to mind the ear-like appendages in Conchoderma aurita 

 (Otion), but these latter are perforated, open into the sack, and point outward. 

 The peduncle-formed body answers, as we shall presently see, to the main part 

 of the shell in Tubicinella, and the hood, as it would appear, to the lips of the 

 sack-aperture, which project between its scuta and terga ; of these valves there 

 is not here a trace. The whole surface is smooth and is formed by rather thin 

 membrane of an orange color; but from the color of the underlying corium 

 the whole appears of a dark chocolate red, the reflexed hood being rather lighter 

 colored. 



The part forming the hood apparently answers to the protuberant lips of 

 the operculum, and the lower part to the subcylindrical shell of Tubicinella; 

 both shell and peduncle in the two genera being wider at top than at bottom. 



