296 HAAS: ABIDA AND CHONDRINA. 



and were restricted to the wider parts of the congosts, which 

 however formed a large part of those I could search on the 

 dry and sterile high flanks of the sierras. On the contrary, 

 the smooth snails, of which the Chondrinas were weak-toothed, 

 were to be found only in the narrowest parts of the congosts, 

 and in the narrow side ravines, in which water trickles down 

 the rocks, and the sun's rays do not penetrate directly. 



All of the folds do not participate equally in the tendency 

 to reduction noticeable in the synopsis of apertural dentition 

 given at the beginning of this discussion. Generally the sim- 

 plification of apertural armature proceeds in about the fol- 

 lowing order : the lower-palatal shows the greatest tendency to 

 disappear; after it comes the infracolumellar lamella. These 

 two are very often lacking together, whereas the presence of 

 columellar and infracolumellar with lower-palatal lacking is 

 one of the greatest rarities, which I found in only three 

 among all of the specimens examined. Of the remaining 

 folds, the upper-palatal is the next to be suppressed. After 

 that, the parietal lamella may disappear, while the angular 

 lamella is the last to go. 



As we have already said, all tooth-combinations do not occur 

 in all localities. Usually those of the first or the second half, 

 or the middle of our tooth-combination table predominate. 

 But not all combinations to be found in one locality are pres- 

 ent in equal strength. Thus among the 450 specimens from 

 El Bruch, with nineteen combinations, there are two dentition- 

 forms with 77 and 217 specimens. Among the 458 specimens 

 from Montserrat, divided between fifteen combinations, two, 

 with 93 and 158 specimens, predominate. 



A striking exception to the examples just mentioned is the 

 typical avenacea, to which all of the 37 specimens from 

 Capellades and 3 from Vallbona belong, to the exclusion of 

 other tooth-combinations. These two localities lie in the valley 

 of the Kio Anoya, tributary to the Llobregat, which appears 

 to be a refuge for C. avenacea avenacea. 



The forms of possible tooth-combinations which have re- 

 ceived names have been sufficiently indicated in our combina- 

 tion table, but a few critical remarks may be added. 



