270 ORIGIN OF LIFE IN AMERICA 



from one another. Dr. Pilsbry divided them roughly into 

 three groups, only one of which inhabits the Antilles. To 

 trace the relationship of the various species to one another 

 seems to be a task even beyond the powers of this distin- 

 guished American conchologist. The minor sections being 

 arranged geographically in Dr. Pilsbry's work, it does not 

 enable us to draw any conclusions as to their former dis- 

 persals. One interesting fact, however, has been brought to 

 light, which proves not only the antiquity of this family but 

 the .extraordinary persistency of specific characters among 

 some of its members. The Oligocene Bulimulus americanus 

 of Florida is practically identical with B. ridleyi, still living 

 on the island of Fernando de Noronha. 



The genus Drymaeus (Otostomus), which is as difficult to 

 classify as Bulimulus, has mainly a continental range. 

 Only a few species live in the West Indies. Among these 

 we likewise notice a remarkable persistency of specific 

 characters. Drymaeus dormani, for instance, occurs in 

 southern Florida, while the closely allied D. dominicus is 

 resident in Haiti, Cuba, Florida, Yucatan, Nicaragua and 

 Mexico. At the first thought we might feel inclined to attri- 

 bute such a strikingly discontinuous range to accidental dis- 

 tribution ; but a careful study of the whole family has im- 

 pressed me with the conviction that we have to deal with a 

 set of very ancient and very persistent types of mollusks. 



Even less satisfactory to identify than Bulimulus and 

 Drymaeus are the Orthalicinae, another large group of Buli- 

 mulidae. Dr. Strebel * has recently undertaken their revision, 

 utilising several characters which had hitherto not been em- 

 ployed in the discrimination of the species. It is an attempt, 

 at least, to trace the complex relationship of the innumerable 

 closely allied forms, although the author does not seem to 

 realize the great antiquity of the group. His arguments in 

 favour of wholesale accidental dispersal, even from western 

 Mexico to the Antilles, are quite at variance with the lesson 

 the study of the West Indian fauna has taught us. Tbe species 

 of Simpulopsis are mostly South American, but a small aber- 

 rant group with smooth apical whorls is confined to Portorico, 



* Strebel, H., " Revision der Orthalicinen." 



