STREPTAXID^E. 55 



The principal conchological character of the group is the sin- 

 gular torsion of the axis of revolution, causing some of the whorls 

 to revolve obliquely to the others. 



The animal has a very long neck and short tail ; the superior 

 tentacles are narrow and long ; the labial palpi narrow, as long 

 as the inferior tentacles ; genital orifice on the right side, distant 

 from the superior tentacle, and closer to the respiratory orifice. 

 Dentition similar to Glandina ; central tooth simple. 



There are about 75 species ; they inhabit warm countries of 

 South America, Africa and Asia, but are absent from Australia 

 and the Polynesian Islands. 



The sections or subgenera of Streptaxis as admitted by Pfeiffer 

 are described in the " Structural and Systematic Conchology," 

 Hi, 16 ; they are rather indefinite groups on account of some 

 species possessing characters intermediate between those upon 

 which the}' are founded. Mr. C. F. Ance} r (Le Naturaliste, vi, 

 508, 1884) remarks that: 



" Pfeiffer and Clessin classify the known species of Streptaxis 

 in these various groups : 



" 1st. Artemon, Pfr. (type, S. candidus) ; 2d. Scolodonta, Doer- 

 ing (type, S. Semperi) ; 3d. Ammonoceras, Pfr. (type, S. ammoni- 

 formis) ; 4th. Eustreptaxis, Pfr., divided itself into two groups, 

 the one comprehending the toothless species, the other those 

 which are provided with a parietal tooth this section is the 

 more numerous; 5th. Odontartemon, Pfr. (type, S. dejectus) ; 

 6th. Discartemon, Pfr. (type, S. discus). 



"It seems to me quite unjust to make in Streptaxis a simple 

 subgeneric group of Ammonoceras, in which the shells are of so 

 different an aspect and hyaline. 



"As to Scolodonta, placed by the author of the group amongst 

 the Helices, I have no opinion, since the species are still too 

 poorly known. 



" The two sections established by these authors in Eustrep- 

 taxis or true Streptaxis, seem to me very artificial; they sepa- 

 rate thus species having the closest analogies. 



" We can, still further, speak in the same way of Odontar- 

 temon ; all the toothed species are placed without order in this 

 section. It seems to me, nevertheless, that it should be preserved, 



