220 MAETIN F. WOODWARD. 



had already been noted by Crosse and Fischer from a study of 

 the shells, and expressed by the institution of the section 

 Perotrochus for the first two species. 



This peculiar specialised area is also to be met with in the 

 Trochidae (notably in T. [Gibbula] magus and T. [Callio- 

 stoma] zizyphinus); but though so commonly present, I 

 am unable to offer any suggestion as to its function. 



The Epipodium. — This structure, which is so charac- 

 teristic of the majority of the Diotocardia, or of that sub- 

 division for which Fischer proposed the name Thysanopoda, 

 is not conspicuously developed in P. Bey rich ii. It takes 

 the form of a couple of folds, one on either side of the body. 

 They start a short distance behind the head and attain their 

 maximum development in the region of the operculum ; 

 whence they extend back in the posterior extremity of the 

 foot, practically meeting in the middle line behind the median 

 dorsal groove. These folds, which are evidently somewhat 

 contracted in the spirit specimen, are like the rest of the 

 body covered with minute papillae, and are entirely devoid of 

 those accessory lapets and tentacles so characteristic of the 

 epipodia of the Trochidas, Haliotidee, and other Thysanopoda. 

 Judging by the figures given by Dall (op. cit., pi. xxx, figs. 

 1, 4, and 5) of the living animal of P. Adansoniana, the 

 epipodium would be more conspicuous in the living animal 

 in P. Quoyana; Fischer and Bouvier even speak of it as 

 being largely developed. In comparison with the Trochidae 

 and Haliotidas, however, I should rather conclude that the 

 epipodium was feebly developed in Pleurotomaria. 



I do not think there is any evidence to support the view 

 advanced by Mitsukuri that these lobes partly envelop 

 the shell, although they are apparently closely applied to its 

 base, and I would rather account for the clean nature of the 

 shell by the habitat of the animal being in deep water — 

 seventy to eighty fathoms, — where life, both animal and 

 vegetable, is not so abundant as in the littoral zone inhabited 

 by the Trochidas, whose shells are so generally encrusted 

 with foreign matter. 



