THE MOLLUSCA HEDLEY. 427 



Beneath the head is a flap terminating anteriorly in two pro- 

 cesses and arising from a deep cleft between the mouth and the 

 operculum. Treating of the same or an allied species from Guam, 

 Quoy and Gaimard* describe this as an anti-buccal appendage and 

 figure it from above. I regard it as the relic of a degenerated 

 propodium. The accompanying sketch (Fig. 17) in profile, of an 

 animal half drawn out of the shell and stript of the operculum, will 

 better convey an idea of this organ than figures taken from above. 



Fig. 17. 



When a gasteropod retreats into the shell it doubles the foot either 

 lengthwise, as in some inoperculate forms, or across, as in most oper- 

 culates. In the latter case when completely retracted, the foot is so 

 folded head to tail that the anterior half of the sole is applied to the 

 posterior ; the operculum then closes the aperture. In a sedentary 

 form this position of retraction might become permanent. Where 

 the foot never serves for progression, but continues to maintain a 

 useful operculum, it is easy to imagine that the fore part of the 

 folded foot would become atrophied and that as it diminished the 

 hind part would enlarge. This is the history suggested for the 

 shrunken propodium of Vermetus, which lies tucked away between 

 the mouth and the operculum. The process of evolution perhaps 

 continued in the direction of utilising the appendices of the pro- 

 podium as tentacles. 



This species was collected by Hugh Cuming at Marutea, Pau- 

 niotus, and opercula of it were received from Lifu by Melvill and 

 Standen. In a preceding article (p. 243) I have quoted a descrip- 

 tion of a mollusc from Mangaiia, called " ungakoa," which is 

 probably this. In Java it is known as " karang," which Morch 

 translates as " coral tube." The only Pacific shell with which 

 this can be confused is the pipe-like Kuphus arenarius, L. 



VERMETUS, sp. 



A second species of this genus, somewhat resembling V. grandis, 

 Gray,f or V. imbricatus, Dunker, also occurred. 



TURRITELLA coNCAVA, Martens. 

 Tryon, loc. cit., p. 206 V pi. Ixiv., fig. 6. 



* Quoy & Gaimard Voy. "Astrolabe," Zoologie, iii., 1835, p. 295, pi. 

 Ixvii., figs. 13 - 15. 



t Tryon Man. Conch., viii., 1886, p. 182, pi. liv., fig. 79. 



