VARICELLA. 47 



tral, not greatly smaller than the adjacent lateral teeth (pi. 

 25, fig. 2). The teeth of V. phillipsi are said to be similar. 



No sharp lines 'Can be drawn- between the three groups of 

 large Oleacinidce here treated as genera, Varicella-, Oleacina 

 and Euglandina, at least with our present very imperfect 

 knowledge of the anatomy of the first two ; yet there is little 

 difficulty in assigning the species to one or other of them. 

 In Varicella the spire is usually more lengthened, the aper- 

 ture shorter than in the other two groups, and the varices 

 or varix-lines are invariably p resent, whereas in Oleacina and 

 Euglandina, they are only rarely developed distinctly. I have 

 elsewhere alluded to the affinities of Varicella and Spiraxis. 



The distribution of the forms indicates an early segrega- 

 tion of the ancestral stock into three phyla. One of these, 

 Euglandina, was evolved upon the mainland with southern 

 Mexico as the probable center of radiation. Oleacina had its 

 rise in the Haiti and East Cuba tract. The third, Varicella, 

 apparently arose in Jamaica, with an early radiation into the 

 Haiti-Cuban area. 



Varicella consists of a considerable number of derivative 

 phyla largely expressed in the degree to which the sculpture 

 has been modified and accelerated. In the more primitive 

 form the embryonic whorls are smooth, as in Oleacina, Eu- 

 glandina, Spiraxis, etc., but in more or less divergent mem- 

 bers of this stock there was a tendency towards earlier ap- 

 pearance of the sculpture (aside from the varices) , pro- 

 ducing several independent collateral phyla with sculptured 

 embryonic s'hells, such as Pichardiella,, Varicellaria, Vari- 

 cellopsis, etc. In both Haiti and Jamaica these groups arose; 

 elsewhere the primitive smooth embryo was not modified. 



The subgenus Pichardiella is perhaps the most distinctly 

 divergent group in the genus, and its wide distribution prob- 

 ably indicates that it was evolved before the separation of 

 Haiti-Cuba and Jamaica. It is noteworthy that this is the 

 only Varicelloid group which has reached West Cuba. In 

 treating of the Urocoptida I have had occasion to show that 

 the snail fauna of West Cuba was largely evolved indepen- 

 dently of East Cuba, indicating separation of the two areas 



