HAAS: ABIDA AND CHONDRINA. 295 



Certain localities afford only a few combinations. Thus, in 

 135 examples from Pobla de Segur, in the valley of the No- 

 guera Pallaresa, the combinations 19 and 20 occur in equal 

 numbers. The smallest example measures: length 6 mm., 

 diam. 2.5 mm., having 7% nearly smooth whorls. The largest : 

 length 10 mm., diam. 3 mm. ; 9 lightly hair-striate whorls. 



Over 300 specimens from the Congost dels Collegats near 

 Pobla de Segur, belong in equal parts to the combinations 11 

 and 14. Smallest measures: length 4 mm., diam. 2 mm., and 

 has 6y 2 lightly rib-striate whorls. Largest: length 5 mm., 

 diam. 2.25 mm., 7^ nearly smooth whorls. This small, slen- 

 der form will be discussed further. 



Valley of the Garona de Ruda in the Valle de Aran, thus 

 on the northern side of the Pyrenees. Over 100 specimens, 

 all with the combination No. 25, the smallest measures, length 

 6.5, diam. 2.5 mm., 6% lightly rib-striate whorls. Largest, 

 length 7, diam. 2.5 mm., 7% strongly hair-striate whorls. 



The measurements cited suffice to show that the variability 

 of the characters considered is considerable, even among speci- 

 mens of the same locality. Consequently they will be found 

 sufficient to explain why I unite under the oldest name fari- 

 nesi all of the mutation-forms of the present Chondrina. 



Although in the course of my collecting I gave serious 

 thought to the discovery of some general relation between the 

 predominance of a certain tooth-combination or a certain 

 average size of shell to a special locality, I could ascertain 

 nothing positive of this kind. Only a single correspondence 

 between the structure of shell and aperture on the one side 

 and ecologic conditions of the station on the other, appears 

 to me demonstrable. In the canyon-like gorges of the pre- 

 Pyrenean sierras, which have been called "congosts," I always 

 found 4-toothed forms of C. avenacea farinesi with more or 

 less strongly striate or rib-striate shells, together with strongly 

 ribbed forms of Pomatias obscurus esseranus Fag., whilst 

 weak-toothed forms of this Chondrina with smooth specimens 

 of the same Pomatias lived together. The stations of snails 

 of the first category are all remarkable for their dryness and 

 lack of vegetation, in consequence of their great insolation, 



