XENOBALANUS GLOBICIPITIS. 445 



Affinities. — This genus presents very varied affinities to Tubicinella, 

 Coronula, and Platylepas. To the latter it is more especially allied in 

 the compartments, being singly folded inwards, though the sides of 

 the folds are not here closely pressed together, as in Platylepas : in 

 both these genera the fold is less deep in the rostrum, of which fact, 

 in Platylepas, the final cause is evident, but here there seems no cause, 

 excepting the simple one of affinity. Xenobalanus is further allied to 

 Platylepas, in the lesser size of the inner fold of each branchia, compared 

 with the outer, and in the structure of the cement-glands, and to a 

 certain extent in that of the sheath. To Coronula the special alliance 

 is shown by the remarkable character of the pseudo-radii lying between 

 the parallel and adjoining walls, and in the general character of the 

 cirri : in Coronula we have the terga sometimes quite aborted, and the 

 scuta of small size, thus exhibiting a tendency to the entire absence of 

 opercular valves, so remarkable in Xenobalanus. To Tubicinella, the 

 alliance is still more plainly shown in the external shape of the whole 

 animal, wider at top than at bottom, — in the opercular membrane 

 descending almost to the very base — in the relative positions of the 

 different parts and organs — in the upper end of the shell continually 

 scaling off — in the prominence of the transverse external ridges — in the 

 sheath being divided into successive zones of growth, and being pro- 

 longed nearly to the basal membrane — and in the edges of the alse 

 being smooth. Internally, the resemblance is also plainly shown, in the 

 strength of the internal tunic of the sack — in the branchiae springing 

 from two approximate fleshy crests — in the freely depending acoustic 

 orifices — in the form of the thorax and prosoma — and consequently of 

 the alimentary canal. 



Seeing the state of the almost rudimentary shell, it is not 

 difficult to imagine its total disappearance. Thinking of 

 this, it occurred to me to doubt for a few minutes, whether 

 Anelasma, described in my volume on the Lepadidse, which 

 presents many points of resemblance with Xenobalanus, — 

 viz., in colour, in the strength of the internal membrane of the 

 sack, in the size of the orifice with its thin membranous mar- 

 gin, in the entire absence of opercular valves, and in epizoic 

 habits, — might not in truth be a. sessile cirripede, in an ex- 

 tremely altered condition ; for the cirri of Anelasma are in so 

 rudimentary a state, and the mouth in so modified a condi- 

 tion, that the internal characters by which pedunculated cirri- 

 pedes can be distinguished from the Balaninae, though not 

 from the Chthamalinee, are almost lost. But if Anelasma 

 had belonged to either of the two sub- families of the Bala- 

 nidse, the sack would have penetrated almost to the bottom 

 of the peduncle ; there would have been only a single layer 

 of longitudinal muscles round the peduncle; and there 



