VIII RADULA OF THE TAENIOGLOSSA 223 



type, but with very long reed-like laterals.^ This singularity 

 was a standing puzzle to the present writer, until he was fortu- 

 nate enough to discover that aS'. spectrum^ unlike all other spe- 

 cies of Sistrum, lives exclusively on a branching coral. 



The dental formula for the Rachiglossa is thus 1.1.1, except 

 in those cases where the laterals are absent, when it is 0.1.0. 



((?) The Taenioglossa comprise 46 families in all, of which 

 the most important are Tritonidae, Cassididae, Cypraeidae, 

 Strombidae, Cerithiidae, Turritellidae, Melaniidae, Littorinidae, 

 Rissoidae, Paludinidae, Ampullariidae, Cyclophoridae, Cyclo- 



^ 



Fig. 125. — Portion of the radula of Cassis sulcosa Born., x 40. The marginals 

 to the right are not fully drawn. 



stomatidae, and Naticidae. The radula is characterised by a 

 central tooth of very variable form, the prevailing type being 

 multicuspid, the central cusp the largest, on a rather broad base ; 

 a single lateral, which is often a broad plate, more or less cusped, 

 and two uncini, rather narrow, with single hooks, or slightly 



Fig. 126. — Four rows of teTfeth 

 from the radula of Vermetus 

 grandis Gray, Andamans. 

 X 4C). 



cusped. The accompanying figures of Cassis^ Vermetus, and 

 Cgpraea, and those of Littorina and Cydophorus given on pp. 

 20, 21, are good examples of typical taenioglossate radulae. 



In Homalogyra the radula is much degraded, the central 

 tooth is large and trianglar on a broad base, the lateral is 

 represented only by a thin oblong plate, and the uncini are 

 absent. In some species of Jeffrey sia the uncini are said to be 

 absent, while present in others. Lamellaria has lost both its 

 uncini, but the radula of the allied Velutina is quite typical. A 

 peculiar feature in this group is the tendency of the marginals 

 to increase in number. A stage in this direction is perhaps 



