1862.] FALCONER PLAGIAULAX. 353 



table-feeding Koala (Fhascolarctus cinereus). The incisor of P. 

 BecTclesii^ is undoubtedly curved more decidedly upward ; and, when 

 viewed sidewise, it is not very unlike a canine. But the same may be 

 said equally of the lower incisor of the Lemurine Aye-Aye (p. 368, 

 fig. 20, a). In this remarkable form, the affinities of which were so 

 keenly disputed by the great Prench anatomists, Cuvier and Blain- 

 ville, the solitary incisors are collateral, on the Rodent type ; com- 

 pressed laterally, and very deep at the base, they sweep upwards 

 in a bold curve, being scooped vertically behind, to terminate in a 

 sharp edge ; so that, regarded sidewise, so far as vertical direction 

 goes, they are more canine-like than in either species of Plagiaulacc. 

 But the resemblance goes no further. In the former the incisor, 

 which is only partially invested with enamel, is continued backwards 

 below the molars, the pulp-nucleus being persistent, and the chisel- 

 shaped edge is constantly maintained by use f — conditions which are 

 wanting in the latter. Should the construction of the skull and 

 other parts of the skeleton of P. Becklesii be ever discovered, there is 

 little doubt but that modifications will be detected throughout, in 

 conformity with those of its incisors, as in the felicitous instance 

 cited by Cuvier, of the secret relation between the upper canine- 

 shaped incisors of the Camel and the bones of the tarsus : this ex- 

 ceptional character does not remove the Camel from among the 

 Ruminants, nor does the form of the incisor of P. BecMesii appear to 

 me to be of sufficient weighb to counterbalance the clear evidence of 

 a phytophagous and rodent plan of construction. 



Professor Owen draws an argument, in confirmation of his view, 

 from the dentition of Thylacoleo. The statement is : — ** In Thyla- 

 coleo the lower canine, or canine-shaped incisor, projected from the 

 fore-part of the jaw, close to the symphysis ; and the corresponding 

 tooth in Plagiaulaoc more closely resembles it in shape and direction 

 than it does the procumbent incisor of Hypsiprymnus "J. But, on 

 referring to his detailed description of Thylacoleo, we find that the 

 body of the tooth, of which the shape and direction are adduced as 

 terms of comparison, together with the fore part of the symphy- 

 sis and incisive border, is wanting §: — ^' The symphysis (pi. 13. 

 fig. 4, s) begins behind, at a vertical line dropped from a little in 

 advance of the middle of the sectorial, p 4 ; it is of a wide and oval 

 form. To judge from the cast, but little of the jaw appears to have 



* Loc. cit., fig. 1. p. 278. 



t Blainville asserts that the incisors of the Aye-Aye are invested all round 

 with a shell of enamel, and that the posterior facet is not the result of wear 

 (Memoire sur I'Aye-Aye, p. 23) ; while Dr. Sandwith, in his interesting ac- 

 count of the habits of this animal, aiRrms that the facet is denuded, as in the 

 Rodents (Zool. Proc, Feb. 22, 1859, p. 111). In a finely preserved cranium, for 

 the transmission of which to London I am indebted to the great courtesy of 

 M. Edouard Verreaux of Paris, it is distinctly seen that the coat of enamel is 

 limited to a belt which sheathes only the anterior half of the incisors. 



X Palaeontology, p. 353. 



§ " Unfortunately, this morceau is much mutilated, the incisor being broken 

 at its entrance into the alveolus ; its form cannot therefore be precisely given ; 

 but it is evident that it was curved upwards." — Stutchbury, Report on the Dis- 

 covery of Gold in Australia, 1855, p. 53. 



