THE AFFINITIES OF PIPISTRELLUS RIDLEYI THOMAS, 1898 AND GLISCHROPUS ROSSETI OEY, 1 95 1 (CHIROPTERA: VESPERTILIONIDAE) By J. E. HILL & G. TOPAL INTRODUCTION In a recent study Hill (1969) examined four further specimens of Glischropus rosseti Oey, 1951, hitherto known in the Uterature only from the holotype and paratype from Cambodia, and concluded that the species should be transferred to Pipistrellus, being alHed to the equally poorly known P. ridleyi, described from Malaya by Oldfield Thomas many years before. Four additional specimens of rosseti have now been found in the collections of the Hungarian Natural History Museum, obtained at Bangkok nearly one hundred years ago by the traveller J. Xantus. Not immediately recognized as rosseti, their external features in particular suggested to one of us (G.T.) that they might represent the genus Myotis, and one skuU was sent to London where its identity with rosseti was estabhshed. There seemed sufficient grounds, however, to justify a further examination of the generic affinities of the two species. Hill (1969 : 138) having considered their features distinctive enough to warrant the estabHshment of a separate group (the ridleyi group) within Pipistrellus. SYSTEMATIC SECTION For many years it remained customary to separate the genera Myotis, Pipistrellus and Eptesicus on the basis (in part) of the premolar dentition, the premolar formula of Myotis being pm|-|-, of Pipistrellus pm|--|-and of Eptesicus pmh-l. In Myotis the central teeth (pm|) are small and sometimes displaced from the toothrows: in Pipistrellus they are presumed to have disappeared and the anterior premolars (pm|-) are frequently much reduced, the upper tooth often displaced. The extent of reduction and degree of displacement has been and is used as a diagnostic feature at the specific level in both Myotis and Pipistrellus, and some authors such as Tate (1942) employ these features as indicators of "primitive" or "speciahsed" species, a greater degree of reduction and displacement being presumed to indicate greater speciahsation, reflecting as it does the extent of shortening of the rostrum from a "primitive" long-nosed condition. Premolar dentition of Pipistrellus and Eptesicus In the last three decades much doubt has been cast on the adequacy of the pre-molar dentition in Pipistrellus and Eptesicus as a diagnostic generic feature, although many years ago Leche (1875 ; 34) mentioned a specimen of Pipistrellus maurus (=P. savii) in which pm^ was rudimentary and barely pierced the gum, and its occasional absence in this species was noted by Miller (1912 : 221). More recently, BuU:_Br. Mus. nat. Hisl.l{Zool.)l2^, g
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