MOLLUSCA. OV INDIA. 23 



species is thin and horny. The example described was collected at 

 Natal, with Balimus Jcraussi, and transmitted to Mr. S. Stevens 

 with other specimens of a smaller size." 



Pfeiffer thus describes the operculum : " tenuissimum, arcti- 

 spirum, corneo-lutescens, extus concaviusculum " ; and the dimen- 

 sions : major diam. 15, min. 12, alt. 8. 



The animal (Plate LXVIII. figs. 1, 1 a), as preserved in spirit, has 

 a blunt square head, the eye-tentacles being short and broad. The 

 foot is also short (fig. 1 e), apparently not extending, even in life, 

 much beyond the circumference of the operculum, whereas in 

 0. aurora it is longer, and in O. crocatus (fig. 5 b) it is elongate. 

 The operculum (tigs. 2, 2 a) is spiral, of 5 whorls, broad and 

 regularly increasing, with a thin edge, slightly concave in front, 

 internally quite smooth, with no indication of a central nucleus. 

 When removed from the animal the scar (fig. 2 o) is also quite 

 smooth, with only a few concentric shallow furrows. The male 

 organ is a solid muscular free sheath, the base (6. P.) on centre line 

 of the neck about 5 mm. from the anal aperture and 7 mm. from 

 the end of the snout, and was found bent over forwards to the right 

 side. It is long, with a broad spatulate end, and the orifice ap- 

 peared when on the slide and under slight pressure to be at the 

 extreme point (fig. 1 d). 



The buccal plates (fig. 3) are strong, similar to those of Cijdo- 

 pliorus, heart-shaped. Under high power (fig. 3 h) the central line 

 is occupied with irregular quadrate-shaped small plates, which 

 merge gradually on the side into the regular rows of placelets, as 

 shown magnified in fig. 3 a ; the comparative size of these little 

 plates varies much in the different species. The teeth of the radula 

 (figs. 4, 4 a) are quite of the character of typical Gtjdophnrux, the 

 central being broad tricuspid, the drst and second hooked and also 

 tricuspid, the third hooked and bicuspid. 



Having no further material from Africa, and nothing from Mada- 

 gascar or the Mascarene Islands, the Nicobars from their position 

 seemed to promise something interesting for purposes of comparison. 

 I next describe one of the largest, and which is also the type of a 

 subgenus of the Cyclophoridae. 



Subgenus Cyclohelix, Morch (1871). (Plate LXVIII. figs. 5-8.) 



Copenhagen, March 1871. 



Type C. crocatus. Born, MiJrch, Journ. de Conch, p. 316, Oct. 

 1872, with no description. 



Nevill, Hand-list, p. 275 (1878). 



H. «& A. Adams, Genera Mollusca, p. 279, as a synonym of 

 Cydoplionts. 



The subgenus Cijdohelix was never described by Miirch, but only 

 indicated. Its principal characters may be thus summarised : — 



