THE SESSILE BARNACLES. 



327 



No further specimens have been found in California, but we have 

 positive records from the Hawaiian Islands. It is well known that 

 the localities of some of Nuttall's Hawaiian and Californian shells 

 were confused. Doctor Weltner has recorded C. liembell from 

 Nagasaki, collected by the eminent conchologist Eduard von Mar- 

 tens ; but I do not know that the specimens have been compared with 

 typical Hawaiian examples. 



Chthamalus hembeli is a rare barnacle in collections. I know only 

 of those in the British and the National Museums, unless the 

 Japanese specimens in the Berlin Museum are correctly identified. 



Genus PACHYLASMA Darwin. 

 1854. Pachylasma DAKWIN, Monograph, p. 475. 



Chthamalidae having a wall of eight compartments, in which the 

 rostrum and rostral latera are united by inconspicuous, linear sutures, 

 or are wholly concrescent in the adult stage, the barnacle thus becom- 

 ing virtually six-valved. Radii wanting or very narrow and not well 

 differentiated from the parietes. Wall-plates without pores, not 

 ribbed within in adults. Basis calcareous. Scutum without an ad- 

 ductor ridge. Caudal appendages present. 



Type. P. giganteum (Philippi). 



These are barnacles of rather deep water, down to more than 200 

 fathoms, in the Mediterranean, oriental, and Australian seas. They 

 are at present rare in museums ; except P. giganteum, each species is 

 known by a single lot from one locality. The several forms sit upon 

 stones, millipores, other barnacles, crinoid stems, and sponges, but 

 to what extent the species are restricted in station remains to be 

 determined. Two species were known to Darwin, and three more 

 have been taken by the Albatross. All are well differentiated spe- 

 cifically. 



It may be expected that with the progress of deep water explora- 

 tion the number of species of Pachylasma and Hexelasma will be 

 very considerably augmented; and I suspect that the division into 

 two genera will become increasingly difficult. The differential char- 

 acters found in the caudal appendages, the labrum, and the basis are 

 less important than might at first be supposed. In Pachylasma, 

 darwinianum the caudal appendages are reduced to a single, minute 

 joint, the basis is extremely thin, and the labrum is not bullate, 



