146 JOURNAL OF CONCHOLOGY, VOL. 16, NO. 5, JANUARY, 192I. 



relatively larger teeth next (in the Upper Cambrian), while the 

 Rhachiglossa, with their few, sabre-like teeth, are scarcely known for 

 ages later (in the Cretaceous), and do not become dominant till the 

 Tertiary epoch. It is a significant fact, that shells of mollusca in the 

 palaeozoic strata are said to show no indication of the perforations 

 due to carnivorous mollusca, so common in our own and Tertiary times. 



It appears probable that archaic univalve mollusca, whether breath- 

 ing by gills or lungs, whether ^ marine, freshwater, or land, were 

 vegetable feeders ; carnivorous habits were a development of later 

 date. The great molluscan .land carnivora, e.g., the South African 

 Aerope, the Central American Euglandina, and the Neozealanian 

 Paryphanta, represent a comparatively recent phase of progression. 

 Food material that is soft and yielding, and which makes no effort 

 to escape its captor, can be satisfactorily held and broken up by a 

 jaw to bite and a number of small teeth to card and mince. Flesh- 

 diet is another matter, especially living flesh, which not only needs 

 stronger and sharper carving-knives to cut it up, but something pre- 

 hensile to hold it still, and neutralise its struggles to escape. 



The land Pulmonata, being more accessible to observation than 

 the marine groups, provide us with excellent illustrations of the fact 

 that transition from a vegetable to a flesh diet is accompanied by a 

 parallel process of evolution in the form of the teeth, on the lines indi- 

 cated above. Although the conditions of life under which the 

 marine groups live preclude equally exact observation, yet the argu- 

 ment from analogy can be effectively employed in their case, and we 

 can hold' that the possession of a radula armed with strong knife- 

 blades is a presumption in favour of the owner being addicted to a 

 carnivorous diet, particularly when his near relations on the shore, 

 whom we can see feeding on- flesh, happen to be furnished with teeth 

 of a like nature.^ 



Thus at one end of the series of land Pulmonata we have the 

 feeders on vegetable matter, whether green or rotten {^Helicidce, Buli- 

 f/iulidce, Urocoptidm, Pupidce, Stenogyridce, etc.), all of which have, in 

 addition to a jaw or jaws, very numerous small, usually square-based, 

 unicuspid or pluri-cuspid teeth, set on each side of a small median 

 tooth. Next come the Liinacidce (e.g., Liinax, Vitrina, Polita, Zonites) 

 a group whose members are known to vary a vegetable diet with 

 flesh-eating on occasion. Here the marginals are profoundly modified, 

 becoming narrower, sharply pointed, uni- or bi-cuspid. In certain 

 cases {Polita) the number of teeth in a row is reduced, while the size 



1 Natica however, or what seems to be N'atir.a, a carnivorous Tajiiioglossate, occurs in 

 very ancient strata. Probably its carnivorous habits are of more recent development. 



2 The Opisthobranchiata and Nudibranchiata, with their variable and complicated radulae, 

 have been omitted from this discussion altogether. 



