Spiraculum, and other tube-bearing Cyclostomacea. 57 



but have been unable to detect any organization corresponding 

 to the vshelly tube. 



It was long since observed by Mr. Benson that no portion of 

 the animal of Pterocyclos appeared to correspond with the pe- 

 culiar incision of the inner, and cowl-shaped process or wing of 

 the outer, peristome. I have examined two or three species* of 

 that genus with precisely the same result. Amongst the Pupi- 

 nidse, I have examined the animals of a variety of Pupina artata, 

 Bens., and of Hybocystis gravida, B., but I could detect no trace 

 of any process similar to that in Raphanlus. 



The question of the use of these peculiar tubes in several 

 genera of Indian Cyclostomacea, and the reason of their exist- 

 ence in only a few forms belonging to two different families 

 (Cyclophoridse and Pupinidse) and by no means closely allied, 

 has always appeared to me of considerable interest. The first 

 and most natural suggestion which would occur to any one is 

 that the tubes in question serve to supply the animal with air 

 when the mouth of the shell is closed by the operculum. But, 

 natural as this explanation seems, and despite its apparent con- 

 firmation by the discovery of the perforated process in the ani- 

 mal of Raphaulus, as described above, a very short consideration 

 will show the difficulty of accepting it. For if additional means 

 of breathing during aestivation are essential to Raphaulus and 

 Spiraculum, how do forms so closely allied to them as Pupina 

 and Pterocyclos contrive to exist without them ? And this is the 

 more inexplicable because there are modifications of the shelly 

 portions of those genera which apparently represent the sutural 

 tubes of Raphaulus and Spiraculum, the close relation of per- 

 forations in the body-whorl and slits in the peristome being 

 show^n by such genera as Scissurella, Haliotis, and Stomalia, 

 Fissurella and Emarginula, &c. Above all, what explanation 

 can be adopted for the tube in Alycceus, perforated throughout 

 its length, but closed at its posterior termination ? 



It is extremely probable that there is a connexion between the 

 existence of the sutural tubes in the land-shells mentioned and 

 the well-known siphon of Ampullaria, which genus, from its 

 habit of sestivating in the dried mud of tanks, and its power of 

 living for months without water, may almost be considered as an 

 amphibious mollusk, and which approaches the Cyclostomacea 

 most closely in the form of the animal. Another siphon-bearing 

 species is Camptonyx, Bens., allied to Otina, which is by most 

 conchologists classed with the amphibious Auriculacese, and I 

 have recently obtained in Western India another generic type 



* Amongst others, Pterocyclos puUatus,^Qns,., from Pegu, P. nanus, ^., 

 from the Nilgiris, and a species (a vaiiety, perhaps, of P. Albersi, Pfr,) 

 from Arrakan. 



