DIGESTIVE ORGANS. 2 if 



oral cavity forms a muscular elevation, which is frequently semi- 

 circular, and above which the O3sophagus opens. Troschel has 

 regarded this as an organ of taste, and from its position it may 

 well have that function. 



For convenience of description the odontophore may be di- 

 vided into five longitudinal areas, which are crossed by the 

 numerous transverse rows of teeth : these teeth are distinguish- 

 able in character in each area. The central tooth is termed 

 median or rachidian, the adjoining area on each side bears the 

 laterals, and these again are Hanked by the'uncini. Sometimes, 

 however, only three areas are found, when the laterals are sup- 

 pressed, and a cross series includes only rachidian and uncinial 

 teeth. In Bullidse again, the rachidian teeth are suppressed and 

 there are simply two bands of uncini. A numerical formula has 

 been devised which represents these teeth thus : 



In Trochus (oo . 5. 1. 5. oo .), meaning 1 rachidian, 5 laterals 

 and numerous ( oo being the sign of infinity) uncini. The mollusks 

 with which we are at present occupied (the Muricidae), have but 

 three longitudinal areas and the formula for Murex, for example, 

 is 1. 1. 1., signifying one rachidian tooth, with a single uncini on 

 either side. The tongue areas bearing the uncini are sometimes 

 designated as pleurae. 



Rev. G. Rowe, 'from whose lucid description the above is ex- 

 tracted,* truly observes that " this subject has been inves- 

 tigated by several naturalists, with a view to obtaining criteria 

 for a systematic arrangement of Gasteropodous Mollusca. Up 

 to the present time, however, their labors have only partially 

 succeeded. The union under one formula of so many creatures 

 widely differing in shells, anatomy and habits, clearly indicates 

 that if the lingual ribbon contains generic characters, they have 

 not yet been ascertained. At the same time it does present 

 differences which may offer collateral evidence in cases difficult 

 of discrimination. It does not help us to discriminate carnivo- 

 rous from phytophagous animals ; but it seems possible to make 

 use of it as a mark between species." 



The teeth, according to the investigations of Leuckart, Bergh 

 and Troschel are composed of ninety-four per cent, organic or 



* Intellectual Observer, v, 67, 1864. 



