L>58 MEKISTIC VARIATION. [PART i. 



fairly regular correspondence. Within the limits of one species p* may 



387. shew great variation : for instance, of Phascologale flavipes 7 



-pecimens were seen : in 1 JT 1 was absent, in 2 it was small, in - mode- 

 i-atf, and in '2 it wa- large. 



388. Didelphys: 7!l specimens normal. One specimen alone, D. lanigera, Colombia. 

 M.. IT.'W, /), was abnormal, having no m* in either upper or lower jaws. 



D. opossum (one specimen, B. M. ) had right m^ larger than the left. 



(4) Molars of certain Macropodidae. 



Tin- following evidence relates to the genera Bettongia, Pot on m* 

 :ind Lui/orcJtestes. Tn these forms the molars are normally four in each 

 ju\v. As THOMAS observes (Oat. Marsup. Brit, ^fus., p. 10~>, /,<,/ ), in 

 /-'- //mii/ia cases of tifth molar occur, but on the other hand cases of non- 

 eruption of m 4 occur also. The variations seen in the three genera 



were as follows. 



4 _ 4 

 Bettongia penicillata : s specimens have m . ; in 7 of them 







///' i- Mnall (in B. M., 279, j, "^ is very minute; but in B. INI., 27S, in, 

 the lo\\er ,,,i is large). 

 '.'!s!>. 1 specimen J has m* in left lower jaw only, this tooth being small. 



B. .A I., L'7!>, rt. 



1.2.3.0.5 1.2.3.0.0 



:;;0. 1 spcfimcn has m T = _. In both upper laws 



1.2.3.4.5 1.2.3.4.5 



tin-re is a small empty crypt behind m 3 , and on right side behind this 

 M-MJII there is a minute tubercular tooth not represented on the other 



side. |J. M., L'79, b. 



4 _ .4 

 B. cuniculus : 2 specimens have m j 



1 specimen lias no left m*. B. M., 982, C. 

 g _ g 



1 specimen lias m- -- = ; in upper jaws m 5 very small in crypts, but 

 D 



in lower jaws they are of good size. B. M. 51. 4. 24. 7. 



4 _ 4 

 B. lesueri : 13 specimens have m - (in one of them m 4 very 



small. B. M., 277, </). 



5 _ 5 

 :!!i. 1 specimen has m m* being minute and lying in crypts. 



B. M., 41, 1K>7. 



4 _ 4 

 Potorous (Hypsiprymnus): /// ; in 5 specimens of P. tri- 



,1,1,'1,/lns ; mid in 2 of 1'. />/<//>/*,, >*. A single specimen of P. gilbert! 

 has no right, upper ///'. B. M., 2^2, b. 



Lagorchestes. In tlii- ^enns /// is present and is a large tooth, 

 not materially smaller than //* :; . Nc\-rtheless it commonly falls short 

 "f 'lie nther teeth and remains partly within the jaw. This was the 

 case in 1<> skulls of /,. 1,'1,,,,-oiilfx and L. i-t>itxj>!r!//<ifntt. In one skull 

 <-f L. /jini-niil' x, ///' stood at the same height as the other teeth. I see 

 no reason to suppose that all the other skulls were voting, and it seems 

 more likely that this imperfect eruption of m 4 is characteristic. 



