xl GEOGRAPHIC DISTRIBUTION. 



extensive Austral continent or " Antarctica," which may have been 

 supplied with these snails as well as with certain marsupials, fishes, 

 etc., from Australia, and subsequently became united at Cape Horn, 

 transferring the fauna. The connection could hardly have been in 

 a reverse order, or why should not Edentates and Hystricomorph 

 Rodents have invaded Australia ? The principal papers bearing on 

 such continental connections in relation to mollusks are those of 

 Hutton, von Ihering and Hedley. It is obvious that the Endodon- 

 tidcB and ffelicidce alone are insufficient to base much speculation 

 upon regarding former extensions of Austral land. A similar ques- 

 tion occurs with regard to the fauna of South Africa, which in the 

 presence of Endodontidce, JKhytididce, Cceliaxis, etc., shows affinity 

 to that of New Caledonia, Australia and Tasmania. The flora, 

 according to Hooker, also has affinities with the West Australian. 



Helicidce-Protogona. This group, as the name implies, is believed 

 to be cearer the ancestral stock of the family than the other groups, 

 mainly, because of the simplicity of the genitalia, which are as in 

 Endodontidce, the less modified Zonitidce, the Rhytididce, etc. The 

 palseontological history of the group is very scant, a few species 

 entirely modern in aspect being found in Miocene strata of Florida. 

 Some forms of equal or greater age are reported from the western 

 United States, but none of them are really known to belong to this 

 group. The references to Triodopsis and Mesodon by writers on the 

 European Tertiary are groundless, the supposed Triodopsis belong- 

 ing to Isognomostoma, the Mesodons to Mesodontopsis, a group near 

 Tac heocampylcea. 



Of the living forms, Polygyra, Polygyrella and Praticolella are 

 exclusively North American, the first named having a few species 

 in the West Indies, and a few which have penetrated from the head 

 valleys of the Missouri to those of the Columbia, and thus reached 

 the northwest coast, the others being East American. There can- 

 not be much doubt that the ancestors of this group of genera have 

 occupied East American soil ever since it had a fauna of ffelicidce, 

 and with the Pyramidulas, to the exclusion of other groups of Hel- 

 ices. In South America the genus Polygyratia occurs ; and while it 

 is likely that its affinities and past history are similar to the preced- 

 ing North American forms, no safe conclusions can be drawn until 

 the anatomy is known. The species from New Guinea and New 

 Ireland, grouped under Coxia, are also beyond the limit of profitable 

 speculation. 



