ri.ASTtO CnARACTEIiS. 



Si/con>/cte)-is iKiias, which h.is lost in, and nr (hotli small in tlio 

 other spt'cios of iho goims), aud JSotopta-ia, which lias lost p' and p 

 (in the related MclonT/cteris and AcnoDi/citris p' is rudiiuoiitarv'). 



Modijications of molar sirwture. — Normally the structuro of the 

 molaritbnn teeth iu Me?:achiroptera is this: a median lonjiitudinal 

 groove flanked by a higher enter and lower inner ridge, eaeh ridge 

 lising (or tending to rise) into a cnsp anteriorly. This typical 

 structure is most clearly pronounced in p' and ni', p^, m,, and ni„. 

 In p-' and p., the outer and inner ringo raises anteriorly into a 

 higher, more narrowly pointed cnsp, and both cusps are either 

 connected at base by a conspicuous commissuro or (very often) 

 completely fused from base to tip, making these teeth iii i)rotile 

 almost eaniniform. If present, ]>', p, and m, are nearly alwavs 

 reduced iu size, and their surface structure more or less de- 

 generated. 



The principal modilkations of the typical molar structuro are 

 due to : (1) the development of a well-marked posterior basal ledge, 

 (2) the development of an antero-internal basal ledge or cusj)! 

 (13) a more or less complete splitting of the outer or inner ridge, or 

 both, into two or more cusps, or (4) the development of surface 

 cusps. If only one of these modifications becomes operative, the 

 general ai>pearauco of the tooth is comparatively little altered; if 

 several (/'/crw/o/),;.!-) or all {JJarpi/ioni/dena) take effect in the same 

 tooth, its appearance is naturally profoundly modilied. 



In rta-opus there is a pronounced tendencv to the developnu-nt 

 of a posterior basal ledge in p', p', p.,, and p„'often also in m' and 

 nip not infrequently in m.^, i.e. the posterior portion of the tooth is 

 more or less distinctly marked off, by a notch in the outer ridge, 

 from the rest of the tooth (fig. 9 B, p. 08; llg. 101], p. (Jil); these 

 posterior ledges are unusually strong in the rurojnis samoensis and 

 pseliqtJwn groups, and in one species of the former group (7'/. 

 anedanus) the ledge is continued forward, as a well-defined shelf, 

 along the inner side of p^ ni„ and ni.^ (fig. 10 C, p. (;9 ; fig. 14* 

 p. 289). In some species of the Ptcro}}iis lomhoccush, samocnsis, 

 and psilajthon groups there arc traces of antero-internal basal 

 tubercles in \)\ p^ p„ and p, or in some of these teeth, i.e. the 

 antero-internal cingulum is some\\hat more ditVcrentiated thuu 

 usual and tending to rise as a small ledge or tubercle. 



Tliese modifications aro further developed and more definitely 

 fixed in Jcerodon (closely related to rUropi.s) : the jiosterior 

 ledges aro always strong, in p^, m,, and m.^ the ledge always extends 

 along the inner base of the teeth as a broad, sh.irply-defined shelf, 

 and a well-marked antero-internal tubercle is always developed in' 

 ])' and m', in some species also iu p' and p^, making these teeth 

 distinctly tricuspid (fig. L'O, p. 413). 



The peculiar molar structure of PUraJojtcv (also related to 

 rtcropux) represents only an extreme phase of the modifications 

 developed in the sjiecies of the rtcropns jisclap/ion group. The 

 teeth are shrM't and broad, the anteii(U- and post(-ri(>r ledges of }>", 



