CHONDRINA. 6 



of Pupillid dentition with lists of the species described. The 

 following are stated to have teeth of the megacheUos-avenacea 

 type: 



algesirae Kob. megacheilos Jan. 



amicta Parr. quinquedentata Born. 



avenacea Brug. scalaris Ben. 



bergomensis Charp. secale Drap. 



bigorrensis Charp. similis Brug. 

 calpica West. 



The inclusion of secale must be due to an error of some sort, 

 as I have found that species to have broad lateral teeth, all of 

 them bearing ectocones. 



Distribution. 



Chandrina, like Abida, is generally found upon rocks, walls 

 and cliffs, preferably on limestone, and therefore is chiefly de- 

 veloped in broken country or mountains, where such stations 

 abound, as are most of the Clausilias. Favorable stations are 

 limited and discontinuous, leading to the segregation of colo- 

 nies of snails having the habits mentioned. 



In distribution, CKondrina is much like Abida, the Alps and 

 the Pyrenees being evolution centers, with one plastic and 

 adaptable species, C. avenacea, widely spread over central 

 Europe. 



About the Alpic center there is the typical or avenacea 

 group of Chondrina, and the section Solatopupa, the similis 

 group. 



In the Pyrenean center and through Spain and Portugal 

 there is the bigorriensis group of Chondrma, and the weakly 

 differentiated section Modicella; both probably derivatives of 

 avenaceous ancestors. Species and races are very numerous, 

 though the structural differentiation has been less, perhaps, 

 than in the Alpic center. The number of species diminishes 

 rapidly westward from the Pyrenees, very few being found in 

 Portugal and northern Morocco. 



It appears reasonable to suppose that an avenacea-like stock, 

 widely spread in southern Europe in late Tertiary time. 



