VERMETUS. 169 



As all three kinds of slit may exist in different parts of a 

 single specimen, the above classification has but little to recom- 

 mend it ; and }^et in a rough wa} r the distinctions of the slit 

 hold good. 



About a dozen species have been recognized by Morch, 

 Sowerby and Reeve. The monographs of the Thesaurus Con- 

 chyl. and Conchologia Icon, are essentially the same ; an earlier 

 one is contained in Chenu's Illust. Conchyliologiques. 



The recent species are tropical and subtropical in distribution. 

 They live on rocks and corals ; the restricted group Siliquaria 

 inhabits sponges. 



Genus CRYPTOBIA, Desh., 1863. 



Proposed for a perforation in polyps, sometimes lined by a 

 shelly plate, sometimes without it ; spire regular, of 5 or 6 

 whorls, in the middle of the polyp ; the following whorls are 

 unrolled ; on one of the walls is found a series of fissures, which 

 traverse the polyp. C. Michilini } Desh., Isle of Bourbon. These 

 perforations are filled by parasitic sipunculi, which may have 

 destroyed in some cases the shell of the mollusk. 



Genus VERMETUS, Adanson, 1757. 

 Subgenus YERMETUS (sensu stricto). 



Typical. 

 V. ADANSONII, Daudin. PI. 49, figs. 20, 21 ; PL 48, fig. 12. 



Shell graceful of 5-12 whorls, loosely or more or less closely 

 coiled, and terminating in a rather straight tube about an inch 

 in length when adult, strongly striated by 6 to 12 raised longi- 

 tudinal ridges or lines, sometimes chagreened ; dark brown, be- 

 coming ash color in dead shells. Operculum very thin, with two 

 small concentric grooves, about half the diameter of the aper- 

 ture. 



Senegal. 

 It is Vermetiis lumJbricalis, Roissy, not Linn. 



Yar. LAMARCKIT, Morch (fig. 21). 



Does not appear to possess any immutable distinctive charac- 

 ter ; the tube is said to be thin towards the mouth, the attach- 



