EXPERIMENTS IN THE BREEDING OF CERIONS. 53 



even obtained Florida key soil and plants in the hope of establishing 

 the microflora upon which these forms seem to thrive and all efforts will 

 be made to keep moisture and temperature conditions as near as possi- 

 ble to the Florida standard. In this conservatory we have segregated 

 pairs as nearly alike as possible, in order to determine, should we be 

 successful in breeding these forms, if a fixation of characters might be 

 effected and new species thus produced. 



In the light of the foregoing results the whole Cerion problem assumes 

 a new aspect. One naturally wonders how this enormously diversified 

 group may have been produced and from what source it was derived. 

 To-day we know members of the genus from the Bahamas, where they 

 are the dominant element in the molluscan fauna. It is here that the 

 genus finds its greatest development. From the Bahamas they extend 

 westward over the Florida Keys and probably over part of the southern 

 tip of the mainland of Florida, then south over Cuba and its islets, the 

 Isle of Pines, the Caymans, Haiti, Porto Rico, and the Virgin Islands. 

 They appear to be absent from Jamaica and the Windward and Lee- 

 ward group, but we again find them represented in Curagao by Cerion 

 uva, and Cerion antoni (Kiister) has been described from Berbice, 

 British Guiana. 



It is unfortunate that the geological history of the group is so incom- 

 plete. At present the oldest-known member of the genus, Cerion 

 anodonta Dall, comes from the Oligocene silex beds at Tampa, Florida. 

 None of the Bahama fossil forms known are older than the Pliocene. 

 The absence of records from the Windward and Leeward Islands leaves 

 a gap in our chain connecting with South America, the cradle of most of 

 our West Indian land shells. Of course it is possible that Cerion, too, 

 may have had its beginning in South America, for our knowledge of 

 the derivation and distribution of other groups, slight as it seems, and 

 the presence of Cerion antoni (Kiister) in British Guiana and of the 

 stranded Cerion uva in Curagao, offer strong suggestions that this may 

 have been the case. 



In a former communication* I pointed out that Cerions could stand 

 4 days of complete immersion in sea-water. This renders it probable 

 that they may have been transported on driftwood. Their occurrence 

 in lowland regions and their habit of affixing themselves to stumps and 

 dead wood during estivation render them especially adapted for this 

 method of distribution. A hurricane might flood a region occupied by 

 Cerions and set adrift 100 or more on a single log, which, after floating 

 for an indefinite period, might effect lodgment in a favorable habita- 

 tion and thus start a new colony. If this is the chief method for long- 

 distance progression, we would have to look to our ocean currents as 

 the determining factor of the direction of Cerion movement. This, of 



*Year Book No. 11, Carnegie Institution of Washington, 1912, p. 131. 



