ABIDA. 263 



their inner ends to form an interior barrier, as in pi. 43, fig. 3. 

 The chief difference, however, is in the teeth of the radula, 

 which are of the normal Pupillid type in Abida, strongly 

 modified in Chondrina. 



The Abidas show far less differentiation in form and aper- 

 tural teeth than the Chondrinas. The genus is also less widely 

 distributed, occupying only the central part of the Chondrina 

 territory, which, except in England, surpasses that of Abida 

 on all sides. 



It had been planned to have Abida and Chondrina mono- 

 graphed by a European conchologist, but this proved to be 

 impracticable under existing conditions. To omit these genera 

 from their proper systematic place seemed unwise, as the 

 monograph of Pupillidse might thus be left incomplete for an 

 indefinite time. Yet to really write a monograph of Abida 

 and Chondrina one should give them some years of investiga- 

 tion; personally collect in several fields, especially in the 

 Pyrenees, in order to get a true perspective of racial values. 

 Finally, the collection of Bourguignat at Geneva should be 

 assiduously studied. It is clumsy work attempting to estimate 

 the species of Dupuy, Bofill, Fagot and other workers in this 

 field, or reconcile their differences, without such preparation. 

 Indeed, I do not presume to do so. It can only be expected 

 of me that the well-established species be properly defined, 

 and a reliable compilation made from the published literature 

 on the others. It is a collection of materials rather than an 

 authoritative monograph. Westerlund's helpful monographs 

 of 1887 and 1897 have been used freely, but the present work 

 comprises many more named forms. With few exceptions, the 

 descriptions have been translated in full from original sources. 



It must not be supposed that the " varieties " herein ad- 

 mitted represent the writer's views. They reflect merely the 

 condition of the literature upon the group. In most cases I 

 have not sufficient knowledge of them for the formation of 

 an opinion. The term "var." leaves the question of status 

 open, and may apply to any subspecific form, whether racial 

 or merely individual variation. A large proportion of the 

 varietal names are invalid, under existing rules of nomencla- 



