258 MERISTIC VARIATION. [part i. 



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



387. shew great variation ; for instance, of Phascologale fiavipes 7 

 specimens were seen ; in 1 jT 1 was absent, in 2 it was small, in 2 mode- 

 rate, and in 2 it was large. 



388. Didelphys : 79 specimens normal. One specimen alone, D. lanigera, Colombia, 

 B. At., 1733, b, was abnormal, having no m 4 in either upper or lower jaws. 



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



(4) Molars of certain Macropoclidae. 



The following evidence relates to the genera Bettongia, Potorous 

 and Lagorchestes. In these forms the molars are normally four in each 

 jaw. As Thomas observes (Cat. Marsup. Brit. Mus., p. 105, note), in 

 Bettongia cases of fifth 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 : 8 specimens have m . ; in 7 of them 



m 4 is small (in B. M., 279, j, ™^ is very minute; but in B. M., 278, m, 



the lower m* is large). 



*389. 1 specimen °. has m 4 in left lower jaw only, this tooth being small. 



B. M., 279, a. 



*onn i • x. 1.2.3.0.5 — 1.2.3.0.0 _ , ., 



*390. 1 specimen has m = — s — = — - — = = — - — =- — . In both upper laws 



r 1.2.3.4.5 — 1.2.3.4.0 rr J 



there is a small empty crypt behind m 3 , and on right side behind this 



again there is a minute tubercular tooth not represented on the other 



side. B. M., 279, b. 



4 — 4 

 B. cuniculus : 2 specimens have m- - . 



391. 1 specimen has no left v?. B. M., 982, c. 



5 5 



*392. 1 specimen has m— — = ; in upper jaws m 5 very small in crypts, but 



o — o 



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 on 4 very 



small. B. M., 277, g). 



5 5 



393. 1 specimen has m , m 5 being minute and lying in crypts. 



B. M., 41, 1157. 



4 4 



394. Potorous (Hypsiprymnus): mj- in 5 specimens of P. tri- 



dactylus and in 2 of P. platyops. A single specimen of P. gilberti 

 has no right upper m\ B. M., 282, b. 



395. Lagorchestes. In this genus m 4 is present and is a large tooth, 

 not materially smaller than m s . Nevertheless it commonly falls short 

 of the other teeth and remains partly within the jaw. This was the 

 case in 10 skulls of L. leporoides and L. conspicillatus. In one skull 

 of L. leporoides, m 4 stood at the same height as the other teeth. I see 

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

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



