202 Mr. T. 11. Withers on some 



Brachylepas, it is certainly interesting tliat Brachylepas 

 should sho\v iu its structure some relationship to the sosile 

 Catophragmus of the subfamily Chtliamulinie. It is much 

 more so when we consider that PolUcipes mitella, vsliich is 

 more closely related in the structure and disposition of the 

 upper valves of the capitulum to Pycnolepas than to any 

 other Cirripede, has also certain definite characters in 

 common with the Chthamalinse. Darwin * drew attention 

 to the fact that P. mitella is more nearly related to the 

 sessile Cirripedes, especially the Chthamalinae, than to any 

 others, except perhaps Lithotrya, and in his Monograph f 

 states the "The Chthamalinae, in the structure of the month 

 and cirri, and to a certain extent in that of the shell, fill uj) 

 the interval between the Balaninae and Lepadidse ; and 

 Catophraymus forms iu a very remarkable manner the tran- 

 sitional link, for it is impossible not to be struck with the 

 resemblance of its shell with the capitulum of Potlicipes." 



It would seem, therefore, that the relationship to the 

 Chthamalinae {Catophragmus) of the fos>ils Pycnolepas and 

 Brachylepas, and of the recent PolUcipes mitella, as deduced 

 by a study of their valves, is supported by the structure of 

 the animal's body iu P. mitella. One miglit also reasonably 

 infer that PolUcipes mitella is the surviior of the group of 

 species iucluded iu Pycnolepas, and that it is independently 

 tending to e%olve into a sessile Cirripede through the 

 suppression of its peduncle and a modification in the lower 

 valves of the capitulum, just as did the early offshoot 

 Brachylepas. 



It is indeed probable that the sessile condition has been 

 arrived at independently on several different lines of 

 descent during the evolution of the Cirripedia. In a pa])er, 

 now iu the press, I have shown that the Verrncidje have 

 a phylogenetic history widely different from that of the 

 Balauidae {sensu lato^, and evidence is not wanting to show 

 that the Ealanidse also are at least diphyletic. The 

 Chthamalinse have almost certainly arisen from some such 

 form as Brachylepas, while it is extremely difficult, if not 

 impossible, to derive the Balaninas from that source or 

 indeed from any form as yet known. 



Zeuymatolepas has already been described in a former 

 paper (Proc. Zool. Soc. London, 1913, pp. 937, 941), and it 



* See Uarwin, C. R., 1S51, Pal. Soc. Mouogr. loss. Lepadidas, p. 48; 

 1851, IJay Soc. Monogr. Cuiipedia, Lepadidse, p. 324. 



t Darwin, C. \i., 1854, llav Soc. Monogr. Cirripedia, Balanidae, 

 p. 48b. 



