THE NAUTILUS. 137 



not find proper conditions for life in the lowlands and the three 

 mountain faunas of the island are almost as effectually separated as 

 when the sea surrounded them. 



The great mountain system of western Cuba (Organos) haa suf- 

 fered rapid erosion and it now happens that whole ranges once a 

 part of the main system have been so cut down by atmospheric forces 

 that they exist today only in the form of more or less detached hills, 

 or " mogotes " as the natives call them. These mogotes, in point 

 of size, may be quite respectable mountains with all the pinnacles 

 and organ-pipe peaks so characteristic of the region, or they may 

 be but a comparative handful of worn down boulders appearing like 

 a little hump on the level landscape. They are practically always 

 heavily wooded and maintaining as they do all the conditions of life 

 needed by the snails, they possess each and every one a little i'aunula 

 of its own, modified, of course, by long isolation from the main 

 range. This accounts in one way for the great richness in Cuba of 

 species. Nature has brought this about by dividing her mollusks 

 into thousands of little preserves and isolating them. As erosion 

 cuts down the mogotes and their quarters become more and more 

 restricted the mollusks that can adapt themselves and fight the battle 

 of life the best, persist, they generally become smaller in size, while 

 others not so adaptable disappear. Thus every mogote has a surprise 

 or two for the collector, usually a new species or subspecies of 

 Urocoptis. 



In most countries there are certain genera of land or fresh water 

 shells that appear to be especially plastic or quick to modify their 

 forms to meet new conditions. In the Bahamas the Cerions, in 

 Europe the Clausilias, in the United States the Pleuroeeratidas and 

 in Cuba the Urocoptis. If these last had received the kind of appli- 

 cation that some genera in other parts of the world have received, 

 there would be in Cuba about a thousand species of them, that is 

 after the mogotes had all been explored. But these Urocoptids 

 have much to tell of what has happened to Cuba in the past. They 

 almost indicate three separate migrations into the island from dif- 

 ferent sources and at different times. One of these may prove to be 

 along a ridge once connecting Cuba through Camaguay, Santa Clara, 

 and the Isle of Pines with Central America, an immigration quite 

 distinct from the one supposedly into Pinar del Rio from Yucatan. 

 Until the land operculates of Cuba shall have been wholly revised as 



