120 "TERRA NOVA" EXPEDITION. 



tlie horizontal plane. It is noticeable that they retain the scaly patches on both rami 

 which are used, by the hermit-crabs which inhabit hollow objects, to give foothold on 

 the inside of their homes. 



With regard to the habits of Porcellanopagurus, some information may be gained 

 from the statements of the naturalists who collected the specimens at present known to 

 science. P. edwarclsi was originally taken in shallow water (down to 5 m.) at Campbell 

 Island and Stewart Island, living among sea-weeds, and was expressly stated by Filhol 

 not to live in a shell. Chilton records it dredged at the Snares in 60 fathoms. The 

 " Terra Nova " specimen, which I have rather doubtfully referred to the same species, 

 was trawled in 70 fathoms off the North of New Zealand, on a bottom of sand and 

 rock. P. platei was obtained on the shore at Juan Fernandez, and Plate, who collected 

 it, stated that it deckt die Eier mit einer Muschelschale zu. Lenz, for no very obvious 

 reason, distrusted Plate's statement, and held that the animal's abdomen kann nach 

 vorn auf den Rilcken geklappt werden, and in that position was mistaken by Plate for 

 the shell of a bivalve mollusc ! This very improbable supposition may be dismissed, 

 in view of the subsequent evidence by which Plate's statement is confirmed for other 

 species. P. tridentatus has been obtained in 54-59 fathoms off Wata Mooli in New 

 South Wales, and between tidemarks in the Kermadec Islands. Oliver, by whom it 

 was collected in the latter locality, found it under stones, and states that it was not 

 common, and that it never uses a spiral shell, but manages to keep on its back a single 

 valve of a bivalve mollusc's shell, or a vacant Sipjhonaria or limpet shell. P. japonicus 

 is as yet only reported from the Uraga Channel in Japan, where a single specimen was 

 taken. No information is available as to the depth or nature of the habitat in which it 

 was found, but it is stated to have carried over its back a Cardium shell, held in 

 position by the telson of the crab fixed in the umbo. 



It appears that Porcellanopagurus has a wide distribution in the extra-tropical 

 parts of the Pacific, that each of the several as yet widely separated localities in which 

 it has been taken possesses its own representative of the genus, that it ranges from near 

 high-water mark to a depth of at least 70 fathoms, and that the same species may 

 extend throughout this vertical range. As will be explained later, while the distinctions 

 and affinities of the species are as yet obscure, it seems that the New Zealand, Chilian, 

 and Japanese forms resemble one another more closely than any of them resembles 

 the Australian-Kermadec species. In most respects there is no indication that the 

 habits of the genus differ substantially from those of the ordinary hermit-crabs, but the 

 mode in which the abdomen is protected is unique among Paguridea. Some kind of 

 shallow, non-spiral shell found by the animal is held over the back, covering, to judge 

 by the extent of the egg -mass, the abdomen and the soft part of the cephalothorax. 

 How the shell is kept in position is not clear. That the telson and uropods should be 

 wedged into the umbo suggests itself at once, and this was the case in Balss' specimen, 

 but if, as Oliver states, a limpet shell is sometimes used, the abdominal organs alone 

 will not suffice to retain the protecting structure. It may well be that the hinder two 



