210 GYLIAUCHEN. 



Genus GYLIAUCHEN Pilsbry. 



Gyliauchen PILS., this vol., p. 174, July 18, 1917. 



The shell is umbilicate, with conic spire of 4 to 5 whorls, 

 the last whorl straightened, becoming free, produced or 

 ascending, as in Hypselostoma. Peristome is expanded. The 

 angular and parietal lamellce are independent and parallel. 

 The plicae and lamellae are minutely spinulose. 



Type : Hypselostoma hunger fordiana Mlldff. 



Distribution : Tonkin and Ava to Kalao and Tenimber. 



This genus differs from Hypselostoma by having an an- 

 gular lamella distinct from the parietal, and by the micro- 

 scopic spinules with which the lamellae and plicae are set. 

 They are most conspicuous on the smaller teeth. Gyliauchen 

 is much more closely related to Paral>oysidia, being merely a 

 further development of that group, differentiated by the pro- 

 duced and partly free last whorl. 



There cannot be any doubt that Gyliauchen and Hypselos- 

 toma are two independent derivatives from Boysidioid ances- 

 tors, their resemblance in shape being due to parallel modifi- 

 cation in the two series. 



Key to Species of Gyliauchen. 



a. Surface minutely rugose or granulose; an excavation or 

 concavity between the upper and lower palatal plicae. 

 &. Last whorl not ascending, shortly free, the upper 

 margin of aperture advanced forward of the lower; 

 alt. 2.6, diam. 2.7 mm. Samui I. G. transitans, no. 3. 

 & 1 . Last whorl ascending somewhat, the aperture look- 

 ing upward slightly, the basal margin advanced. 

 c. Diam. 2.5 mm. ; spirally striolate. Samui I. 



G. striolatus, no. 4. 

 c 1 . Diam. 3 mm. or more ; surface granulose. 



d. Neck long ; aperture with several lamel- 

 lae between the parietal and columellar. 

 Perak. G. hungerfordianus, no. 2. 



d 1 . Neck moderate or short; aperture dis- 

 tinctly looking upward. 



