128 AMPHIDROMUS. 



are very closely allied, in fact, not everywhere clearly differentiated, 

 and Xanthomelon and Albersia seem also to be near them. Cam&na 

 and Obba form another group within the subfamily, while Ganesella, 

 Papuina and Amphidromus, the latter two arboreal, stand somewhat 

 isolated. In the angulated rows of teeth and their broad cusps, Am- 

 phidromus approaches Papuina and Polymita* Whether these fea- 

 tures are purely adaptive or indicate a relationship with the former 

 genus, remains to be seen. 



In most of the species of Amphidromus the nepionic shell appears 

 quite smooth ; but in a number of the smaller sinistral forms, such as 

 the A. sylheticus group, some sparse, elongate, shallow pits or punc- 

 tures may be seen. 



While Amphidromus had formed the subject of special studies by 

 PFEIFFER and MOUSSON, it was Professor E. VON MARTENS who 

 produced the first essay of marked ability. In his volume on the 

 land snails of the " Prussian Expedition to East Asia" (1867, pp. 

 77 and 332), the general characteristics of the group are discussed, 

 and a large number of species reviewed with masterly grasp of the 

 subject. This sound and sane work of the Berlin savant remains 

 to-day undiminished in value. 



In the *' Annals and Magazine of Natural History " for January, 

 1896, Mr. Hugh Fulton published "A list of the species of Amphi- 

 dromus Alb., with critical notes and descriptions of some hitherto 

 undescribed species and varieties " (pp. 6694, pi. v, vi, vii), in which 

 .the sixty-four known species are classified in some nineteen "groups," 

 with many useful notes, descriptions and figures of species and varie- 

 ties not before illustrated, among them the types of Pfeiffer's unfig- 

 ured species. This catalogue is a work of great practical utility and 

 has been very serviceable to subsequent investigators. 



The variability of species of Amphidromus has been discussed by 

 von Martens, whose observations go so directly to the point that I 

 partially transcribe them in the two paragraphs following. 



The group owes its name (^Amphidromus, running both ways) to 

 the peculiar circumstance that several species occur either dextral or 

 sinistral, with equal frequency ; others are sinistral only, still others 

 dextral ; so that the difference in direction of the coil, which usually 

 is characteristic of whole genera, or appears as a rare monstrosity 

 in a species, sinks here to sometimes only an individual characteristic, 

 sometimes merely specific. 



