STREPTAXID^E. 53 



columella with a spiral plication, outer lip externally inflected 

 and strongly angulated in the middle, bearing a strong tooth; 

 yellowish white. Length, 3*25 mill. 



Los Roques (east of Cura$oa) West Indies. 



I am not aware that the dentition of the mollusk of this 



curious little shell has been examined, but it has been placed in 



the Agnatha on conchological grounds by Pfeiffer, Binney, etc. ; 



its general aspect is nearly related to that of Volutaxis. 



FAMILY STREPTAXIDjE. 



Shell heliciform or pupiform, the last whorls generally devia- 

 ting obliquely from the others. 



Animal with a long neck and short tail ; superior tentacles 

 long and narrow ; labial palpi narrow, moderate. Dentition 

 resembling that' of Testacellidse. No jaw. 



Dr. Stoliczka (Jour. Asiatic Soc., xl, 159) remarks upon the 

 family as follows : 



"Dohrn in 1866 (Mai. Blatter, xiii, 129), proposed to unite 

 Streptaxis, Ennea and Streptostele into a separate group, for 

 which he suggested the name Streptocionidse. There does not 

 appear to be any reason why we should deviate from the gener- 

 ally introduced custom of selecting the family name from that 

 generic one which includes the most typical forms of the group, 

 and this genus is in the present case Streptaxis. The family has 

 already been pointed out by Dr. J. E. Gray, in 1860 (Ann. and 

 Mag. N. H., vi, 268), under the name Streptaxidse. 



" The three above-noticed genera (each of which includes 

 several characteristic sections) have the following characters in 

 common : a thin hyaline or a thicker alabastrine shell with very 

 thin, deciduous epidermis, an expanded lip of the aperture, pro- 

 ducing in the course of growth a transverse costulation of the 

 whorls, the last of which usually somewhat deviates from the 

 axis of the spire ; the columella is always thickened and often 

 toothed, or provided with a projecting lamella. 



" Dohrn appropriately pointed out the striking relations of the 

 shells of the three genera by quoting the following parallelism : 



