THE SESSILE BARNACLES. 279 



are irregular in occurrence and arranuenient, and many of them do 

 not reach the periphery. Finally, the sheath is grooved transversel}'^, 

 as in TubiciTiella and Xenohalanus. 



"With the exception of the grooves of the sheath, nearly all of these 

 differences from Coronula are degenerati\e changes apparently cor- 

 i"elated w'lilx the protected station of the animal embedded in the 

 skin of the host. An outer Avail is no longer needed. The branches 

 of the ribs, which in Coronula serve as buttresses, have become short 

 and extremely variable. In fact, the form and size of the ribs them- 

 selves vary ^emarkabl3^ The increase in number of parietal ribs or 

 folds over that in Coronula eompJanata probably toolv place through 

 the accelerated branching of sutural folds, bringing the lower 

 branches down to the circumbasal border, where they appear as 

 primary folds. The circumstances are similar in many phyletic 

 series of shells, in which external ribs become emarginate, then bifid, 

 and finally separate ribs. 



It may be concluded, therefore, that Cryptolepas is a derivative of 

 the Cetopirus branch of Coronula and that its differential charac- 

 ters are mainly due to the degeneration of protective and strengthen- 

 ing structures, now useless because of its deep embedment in the 

 skin of the host. 



But one species of Cryptolepas is known. Cryptolepas ophlopJiilus 

 Kriiger is a member of the genus Platylepas. 



CRYPTOLEPAS RACHIANECTI Dall. 



riiite G6, figs. 1-00. 



1872. Cryptolepas rachianecti Dall, Proc. California Academy of Sciences, 

 vol. 4, p. 300. 



1874. Cryptolepas rachianecti Dall, in Scammon, Tlie Marine Manmials of 

 the Northwestern Coast of North America, p. 22, pL 10, fig. 6. 



1903. Cryptolepas rachianectis Dall, Gruvel, Nouvelles Archives des Muse- 

 um, ser. 4, vol. 5, p. 153, pi. 2, figs. 4-10 ; pi. 3, figs. 10, 11. 



1905. Cryptolepas racliianectis Dall, Gijtjvel, Monographic des Cirrihipedes, 

 p. 274, fig. 299. 



T7/pe.~C3it. No. 9192 U.S.N.M., from Monterey, California. 



Distribution. — Bering Island to Lower California ; Hawaiian 

 Islands.^ 



The barnacle is almost wholly embedded in the whale's slvin, 

 " usually on the head and fins," only the opercular membrane and 

 parts of the radii or sometimes the more prominent ribs being ex- 

 posed. When the skin is removed, four to six ribs are seen on each 

 compartment above. These ribs are denticulate along both sides. 

 In basal view the ribs are seen to be loops of the wall, as in Coronula. 



^The last locality is given on the authority of Professor Gruvel, who found specimens in 

 the Paris Museum. 



