1^93.] Dil. C. J. rOllS^TH MAJOll ON xMlOCEisE Sii^UlllEELS. 207 



a cardinal point and will, wheu once generally recognized, appear 

 to be a simple truth, 



Bunodontv, as opposed to lophodonty, is the iirst step from a 

 transverse arrangement towards the longitudinal one, and is not 

 always to be distinguished at once from the second step 1 aui 

 speaking of, though this last is often characterized by a sort of 

 asymmetry, or confusion, in a \\"ay, as is usually the case in 

 transitional stages. 



First, as to ^ciurina'. As has already been said, transAerse 

 crests are to be found oulj^in semi-hypsodont tyj^es, many of \A"liich 

 tend towards the Hystricomorpha, which for their lack of bracliy- 

 dont molars at once shoA\' themsehes to be more specialized forms. 

 ^,Vhh. the exce])tion of Myoxine types — and this exception is only 

 an apparent one — we may say that the more the molars tend 

 to\\ards brachydonty, the more the crests are broken up into cusps. 

 Of these cusps there are generally five on the outer side of upper 

 molars, two or three of Mhich ha^e been prominently developed. 

 In the middle two intermediate, and on the inner side in the same 

 manner as on the other side, originally a loiujltiulinal series of 

 cusps were developed, which A^ery soon, viz.,Avhen the tooth ceases 

 to be perfectly bi'achydont (as well as in somewhat worn semi- 

 hypsodont or hypsodont teeth), are reduced in number and tend to 

 become coalescecl, a middle cusii appearing the most developed. 

 This middle cusp seems to be for the greater part the remnant of 

 a fifth series \\hich ha^e become partially atrophied, in order to gi\ e 

 place for the median trans\erse valley ; and it is in consequence 

 of the formation of this valley that the cusps appear arranged 

 ill transverse series, even before being connected as ridges or 

 crests. 



Ill superior and inferior molars, the most brachydont members 

 of the family are at the same time those which show a tendency 

 towards a longitudinal alignment of their cus])s. The difference 

 bet\A"een superior and inferior molars consisting in the presence in 

 ujjper molars of intermediate cusps, in more specialized, viz. less 

 brachydont forms, geuerally reduced to t\Ao, as before stated, but 

 which, as slioun by llie most brachydont forms, are the remnants 

 i)f one or more longitudinal series of cusps or tubercles, inter- 

 mediate between the outer and the inner series. 



The cup- or basin-like shape of inferior 8ciuromorphine molars 

 is but a slight specialization of a primitiAe ty])e, a disposition of 

 the cusps on the outer and inner margin, Avith an iuterAeuiug 

 longitudinal depression. The slight specialization consists in the 

 begiu]iing of a transverse arrangement. In the Bornean lildthro- 

 .s-fut/'«s (Plate 1.x. fig. 2), the whole of the very brachydont iuferior 

 molars consists iiuiinly of two series of margijial cusps, none 

 specially developed, and with a spacious longitudinal groove dividing 

 the outer from the inner series; thus pointing significantly to- 

 AA'ards some primitive mammalian molars remote in time (Mici'O- 

 Usles). And so the curious I'.'fcii'/osciuras, from the Upper Eocene 

 of Southern Germany, shows the tendency towards, or, as we rathe 



