— 350 — 



posteriorly ; the fifth low and siender, its anterior half 

 oblique, its posterior half nearly horizontal and also with 

 a slight denticle posteriorly ; ail five united by a low vert- 

 ical callus, and distinctly visible outside through the 

 shell w^all. 



Diam. maj. 7, min. 6,25 mm. Alt. 4 mm. (type). 

 — — 5.75— 4,75 — — 2,5. 



Hab. : Ha-Lang, Tonkin. 



Type in the collection of the School of Mines, Paris. 



This, the smallest known member of the genus, is allied 

 to P. Anceyi, but in addition to being smaller than that 

 species, ithas a more elevated spire, lacks the spiral striae 

 and has a glossy base. In the pariétal armature it difïers 

 in the more obliquely descending posterior plate, and in 

 the présence of a free fold below the anterior vertical plate 

 and a horizontal fold given ofï from the upper extremity 

 of the anterior plate. In its palatal armature it difïers in 

 having only five folds instead of six and they are much 

 less attenuated, the four lower ones being provided with 

 a minute denticle posteriorly. The pariétal armature 

 somewhat resembles that of P. tennis, but difïers in having 

 the upper horizontal fold united to the anterior plate, 

 whereas in P. tennis that plate is free and much shorter. 



A spécimen with more elevated spire and having, the 

 entering fold on the pariétal wall further back, uot united 

 to the pariétal ridge, appeared atfirst distinct ; the palatal 

 barriers, moreover, could be seen much further back, 

 being in the middle of the last whorl. On breaking away 

 a part of the shell wall I was surprised to find the pala- 

 tal and pariétal barriers some distance apart, the latter 

 being in the normal position, and a doser inspection re- 

 vealed the fact that the palatal folds were those of an 

 older séries, the corresponding pariétal plates being 

 nearly absorbed, their bases being just discernible ; of 

 the later séries the pariétal barriers are complète, but of 



1 



