HAAS: ABIDA AND CH0NDR1NA. 275 



specimens with thickened peristome can be found. Thus it 

 will be understood that a full-grown Abida with all the aper- 

 tural folds the species will have, need not by any means have 

 completed the construction of the shell. If it lives in a favor- 

 able spot, that is, where lime is abundant, it will continue by 

 degrees to add to the peristome until it becomes continuous 

 and, according to its kind, reflected or thickened. Also the 

 folds and teeth of the aperture increase in strength under 

 such circumstances. However, as the average collector and 

 also the describing author, who seldom collects personally, 

 considers a snail adult when it has finished its increase in 

 size, so he may often describe as a new variety or even species 

 a pupillid which is of full size, but has not reached the full 

 formation of the aperture. Such cases have unfortunately 

 been introduced very often by the young adherents of the 

 Bourguignat school; and also Westerlund has shown his lack 

 of personal experience as a collector by naming immature 

 snails. 



The fundamental mistake, however, which has led to all this 

 introduction of needless names, is that authors have thought 

 that they must slavishly hold to the original descriptions, and 

 demand that every species must agree in all details therewith. 



This theoretic digression was necessary to explain why I 

 attach little or no importance to differences in the develop- 

 ment of the peristome or in the strength of the apertural 

 armature, and why I do not recognize forms which have re- 

 ceived names on the ground of such differences. 



Pupa Ugerrensis M.-T. (Vol. XXIV, p. 280, pi. 43, fig. 11) 

 I consider a not fully-formed A. ringens; and as explained 

 above, the name bigerrensis must now be used for what has 

 hitherto been considered typical ringens. Pupa baillensi 

 Dupuy (Vol. XXIV, p. 280) is also an uncompleted, but 

 shorter and thicker A. bigerrensis {ringens). A specimen of 

 A. ringens var. baillensi identified by Boettger, from Bayonne, 

 the type-locality, is figured on pi. 23, fig. 10. P. garumnica 

 Fagot, from the upper Garonne region, treated by Pilsbry as 

 a variety of baillensi, is larger than this, and has a more 

 broadly expanded peristome. A specimen collected by Bofill 



