HYPSELOSTOMA. 175 



Genus HYPSELOSTOMA Benson. 



Tanystoma BENS., Ann. and Mag. N. H. (2), xvii, p. 130, 

 Feb. 1856; not of Latreille, 1829 (Diptera). Hypsclostoma 

 BENS., t. c., April, 1856, p. 342; monotype T. tubiferum. 

 Tonkinia J. MABILLE, Bull. Soc. Malac. France, iv, 1887, p. 

 123 ; monotype T. mirabilis. 



The shell is umbilicate, spire conoidal, elevated or depressed, 

 spirally striate; the last whorl angular or carinate, becoming 

 free, the free portion more or less ascending, straight or 

 twisted upward; aperture varying from subvertical to hori- 

 zontal and looking upward, usually toothed, the angular and 

 parietal lamella wholly concrescent into one irregular lamella; 

 peristome expanded. Animal externally as in Gastrocopta, 

 having long eye-stalks and short tentacles. 



Type H. tubiferum (Bens). 



Distribution : Burma, Tonkin, etc., the Loochoo Islands and 

 Philippines. 



According to Blanford and von Mollendorff the Hypselos- 

 tomas are rock snails, living on limestone, generally covered 

 with lime dust. They nestle in cracks and holes, and often 

 are hard to see. 



Hypselostoma differs from Gylmuchen by having the an- 

 gular and parietal lamellae concrescent into a single bilobed 

 lamella. It is a more evolved genus than Gyliauchen, which 

 retains the primitive structure of two parallel lamellae. The 

 lamella? and plica? of Hypselostoma are never spiniferous. 

 The genus was apparently derived from Boysidioid ancestors, 

 and differs from Boysidia chiefly by the free last whorl ; also 

 by the spiral striation, which, however, is almost obsolete or 

 relegated to an early neanic stage in some species. 



The chief teeth are usually placed in form of a cross, the 

 parietal and lower palatal, the columellar and upper palatal 

 being symmetrically opposed. The basal fold is very often 

 wanting, but the upper palatal plica is, with few exceptions, 

 larger and more constant than in Gastrocopta. 



In H. tubiferum, H. mirabile and H. roebeleni the last whorl 

 is twisted upward, bringing the plane of the aperture nearly 

 parallel to the equatorial plane, and elevated above the de- 



