TURRITELLID^. 79 



being sometimes broken off, so as to make the centre 

 pervious. 



This species may possibly have been the Dentalium mi- 

 nutum of Linne^ from Plancns. It is the Odontostoma 

 lavissima of Cantraine ; and it is the Brochus glabrus and 

 B. Icevis of Brown, the young being his B. arcuatus, and 

 the fry his Cornuoides major and C. minor. Adams 

 [' On the Microscope ') named the last-mentioned state 

 of growth Serpula incurvata; and Montagu called it 

 (from another of Walker^s figures, showing the centre 

 whorl broken off) Vermiculum pervium. Sars does not 

 believe the S. incurvata of Adams can be the young of 

 C. glabrum, because he has found specimens of each 

 equally large ; but it must be borne in mind that the 

 adult are of different sizes, and that many species of 

 mollusca have a dwarf or small variety. Besides, when 

 the spire is truncated and gone, the shell becomes pro- 

 portionally shorter, although it increases in diameter. 



Family XIII. TUKHITEL'LID^, Clark. 



Body elongated : mantle forming a slight canal or fold in 

 front : head snont-shaped : tentacles cylindrical : eyes outside 

 the tentacles, at their base : foot short : gills consisting of a 

 single plume. Hermaphrodite ? 



Shell spiral and turreted, many-whorled, not umbilicate : 

 spire tapering, with a blunt apex : mouth having a thin and 

 llexuous outer lip : operculum horny and circular. 



The founder of this family afterwards sacrificed it by 

 uniting it with Vermetidas. Most conchologists, how- 

 ever, think they ought to be separate. The Turritellidce , 

 in all probability, subsist on animal food. 



