XX HISTORICAL SKETCH. 



The publication of Albers' Die Heliceen, in 1850, marked a dis- 

 tinct advance in the discrimination of natural groups throughout 

 the land snails ; but the general principles followed do not differ 

 radically from those of Beck. In 1855 PfeifFer published a some- 

 what amplified arrangement, with some new subgeneric names ; and 

 in the same year the brothers Adams reached the Helices in their 

 Genera of Recent Mollusca. The classification adopted in this work 

 differs widely from previous arrangements; but as its original 

 features are nearly all either retrogressive or founded upon fallacious 

 characters, the generic and subgeneric scheme need not be quoted 

 here. Reeve's monograph of Helix in the Conchologia Iconica 

 (1851-1854) supplied the first illustrations of a multitude of species, 

 chiefly those of Pfeiffer. Dr. Binney's Terrestrial Mollusks of the 

 United States (1851-1857) gave a magnificent series of plates of 

 American forms, among the best portraits of snails ever published ; 

 and the work of Dr. Joseph Leidy therein, was the first anatomical 

 investigation to be made on American Mollusks. 



In France, Moquin-Tandon was preparing a faunal work of the 

 same thorough character, which was issued in 1855, with sumptuous 

 colored plates and well-drawn anatomical details of the snails of 

 France. 



Simultaneous with the last, Adolph Schmidt published his Ges- 

 chlechtsapparat der Stylommatophoren in taxonomischer Hinsicht 

 (Berlin, 1855), a classic work, ranking with that of Semper in the 

 grasp of principles, and laying a broad foundation for the compara- 

 tive study of snail genitalia. Schmidt establishes upon anatomical 

 data the groups Pentatcenia (=Helix s. str.), Fruticicola, Xerophiia, 

 Campylcea, shows the true relationships of the carthusiana and 

 numnws groups and of H.pisana and personata, separates H. obvoluia 

 from the personata group, etc. Many of these notable improvements 

 in classification have since been completely lost sight of by recent 

 European conchologists, and are only of late fully appreciated. 



The work of Schmidt belongs to the Beckian period only chrono- 

 logically. In insight and genius it is altogether modern. 



V, 1860- . ALBERS-MARTENSIAN EPOCH. While several 

 works of the decade preceding 1860 were far in advance of the stand- 

 point of Beck, yet their scope was not sufficiently wide to create any 

 general change in the views of Helix classification held in various 

 countries. The appearance of the second edition of Albers' Die 



