460 MR. ^r. F. WOODWAHD 0>' MA-MMALIAX DEXTITTOX. [May 2, 



through the region of the 1st molar at two stages, show (fig. 25) 

 that there is present on the outer side of the enamel-organ a 

 conspicuous outgrowth of its cells extending down into the gum at 

 right angles to the swollen portion of the denial lamina. This mass 

 takes its origin from the dental lamina nearer to the surface of the 

 gum than the point of origin of the molar tooth, which condition is 

 apparently just the reverse to that which we have seen in the incisor 

 region, where, if there was a rudiment of a second set of teeth, it 

 was situated internal to, and deeper than, the functional one, and 

 represented a replacing dentition. Here in the molar region, on 

 the other hand, we can only interpret these appearances on the 

 grounds that the functional molars belong to the 2nd or replacing 

 dentition, and that this downgi'owth on their outer sides represents 

 the rudimentary, or rather vestigial, milk or 1st dentition. I may 

 perhaps mention here that I ha^■e found what appears to be a 

 similiar condition in Putorius and C'avia, while in Lepus and Taljja, 

 where there is a suggestion of the reverse condition, we are in 

 reality dealing A\ith the dental lamina itself and not a downgrowth 

 from it, as may be seen A\hen the more posterior sections are 

 examined. 



The second species of l^ti-oi/cdt, ^\■hich was evidently the more 

 advanced embryo of a smaller form, sho\^•ed only t^o vestigial 

 upper incisors, these having the relation of i^ and ?"*, and one only 



in the lower jaw, viz. i^ ; it may be that 7- were already reabsorbed. 



Maceopus beachyueus. 



Two specimens examined, measuring respectively 100 mm. and 

 135 mm. 



These specimens, although so small, were A-ery much older than 

 the Petrogales described above, Macropvs hrach>/nrus being one 

 of the smallest Wallabies ; the teeth were in consequence much 

 more highly developed. 



Only two vestigial teeth were present in each premaxilla, 

 corresponding in position AA"ith P and f : the former was of 

 considerable size and so close to the surface of the gum that it is 

 just possible that it is shed in this form ; the latter was, on the 

 other hand, very small and already partially absorbed. 



The three functional incisors (P, i\ and i^) all exhibit slight but 

 distinct downgrowths from the inner side of their enamel-organs 

 representing rudiments of the successional teeth, according to 

 Kiikenthal's theory, and are therefore, as in all Macropids, referable 

 to the 1st dentition. 



In the lower jaw there are present 2 pairs of incisors represent- 

 ing ij and i.^. The first being a vestigial tooth but of fair size and 

 well calcified ; the second is the large incisor of the adult and 

 shows an epitheloid cord on its inner side representing the 

 successional tooth. 



No trace of a canine was visible in either jaw of this specimen, 

 the anterior premolar, Mhich is here very large, coming close behind 



