271 



THE TEETH OF SNAILS. 



BY 



Major A. J. Peile, R. A. 

 (With one Plate.) 



Almost all the mollusca, except the bivalves ( Pelecypoda ) possess 

 in the mouth and throat an organ which is sometimes referred to 

 as the palate or the tongue, but which is better called the " radula " 

 or " odontophore." Only a few genera do not possess this apparatus 

 and these are mostly parasitic in their habits and obtain their food 

 by suction of the juices of their hosts. , 



The radula consists of a band of chitin studded with rows of 

 teeth, each row generally bilaterally symmetrical on either side of a 

 centre tooth. The band lies on the floor of the mouth and is flat in 

 the for\\^ard part, but further back often forms almost a* tube. The 

 shape, number and arrangement of the teeth differ enormously in 

 different families and even in different genera, so that a study of 

 these beautiful objects is of great interest as affording ,an insight 

 into the natural affinities of the group. 



An excellent account of the organs in question is to be found in 

 the Cambridge Natural Histoiy, Volume " Mollusca." These few 

 notes, which are based on the arrangement given in that volume, 

 are explanatory of some of the types which have been mounted for 

 the Society's collection. These were obtained, with one exception, 

 from spirit specimens furnished by the kindness of some of the 

 members. The illustrations are from photographs and drawings of 

 the actual specimens. 



A. SCAPHOPODA. 



The collection does not as yet possess a radula of this class. Some 

 of the DentaiidcB (tusk shells) are found at Bombay, notably the 

 small Cadueus gadus, Sowerby, common as dead shells in shell sand. 

 The living animals burrow in sand and mud. 



B. Gasteropoda. 



1. Order Pulmonata. — This order contains the inoperculate 

 land and freshwater snails. These possess a radula consisting of 

 numerous rows of minute teeth each on its own basal plate, so that 

 the whole structure resembles the surface of a rasp. Example : Ario- 

 jpltanta Icevipes, Miiller, the common striped snail of Bombay with a 

 sinistral shell. Plate, fig. 1, shows a portion of the radula; at 

 the edge on the left side, where the membrane has been doubled on 

 itself, the hooked form of the teeth may be discerned. Text, fig. 1, 

 shows the form of the central tooth of each row and the adjoining- 

 laterals ; fig. 2 shows the change in form of the teeth as the edge 

 of the radula is approached, the lateral passing into so-called 

 marginals. 



