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 1 free, produced or 

 ascending, as in Hypselostoma. Peristoine is expanded. The 

 angular and parietal lamella are independent and parallel. 

 The plicse and lamellae are minutely spinulose. 



Type : Hypselostoma liungerfordiana 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 Paraboysidia, 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. 



eZ 1 . Neck moderate or short; aperture dis- 

 tinctly looking upward. 



