155 



peculiarities of the cranium, and especially the condition of the dental 

 system. 



In both the adult crania the dental f ormula was as follo\vs : 



Incis. j3-į, canin. g^, pramol. j^, mol. ^ = 30 : 



it thus corresponds numerically with the formula of the genus Hy- 

 psiprymnus, and difFers only in the absence of a few minute, incon- 

 stant, and functionless teeth from the dentition of many of the Pe- 

 taurists and Phalangers. The true molares in the Koala are, how- 

 ever, relatively larger and stronger than in the Potoroos and Pha- 

 langers, yet present the šame general structure ; each molar is beset 

 vith four three-sided pyramids, the sharp apices of which soon be- 

 come blunted by trituration, and the outer series in the upper grinders 

 are the first to be worn down ; the posterior grinder is a Httle smaller 

 than the ręst in the upper jaw ; the true molares of the lower jaw 

 are equal amongst themselves, but narro\ver than those of the 

 upper jaw. The crowns of the pr<emolares, or falše grinders, are 

 subtriangular, broadest behind, compressed, and terminate in a cut- 

 ting edge ; those of the upper jaw have a ridge extended along the 

 inner side of their base ; they do not exceed in antero-posterior ex- 

 tent the crovvns of the true grinders. The true molares of the upper 

 jaw have four fangs ; those of the lower jaw, and the preemolares in 

 both jaws, have two fangs. The canines are situated close to the 

 maxillo-incisive suture, distant from the praemolares half an inch ; 

 they are very small, and do not extend beyond the alveolar margin 

 further than two lines ; they terminate in an obhque cutting edge, 

 and their simple fang is closed at its extremity. Two lines anterior 

 to the canines begin the series of incisors, of which the four posterior 

 ones are of the šame size as the canines ; the pair immediately behind 

 the large anterior incisors have their crowns worn flat by the appulse 

 of the two large incisors below. The two anterior incisors, upper 

 jaw, are twice as long, and as broad and thick as the posterior ones ; 

 their crown is conical, slightly curved, subcompressed, beveled off 

 obliquely to an anterior cutting edge, and having a partial coating 

 of enamel, but differing from true dentes scalprarii in having the ex- 

 tremity of the fang contracted and closed. The two incisors of the 

 lower jaw are longer, straighter, and more compressed than the cor. 

 responding pair above ; the enamel is confined to the anterior and 

 lateral surfaces of the crown ; but this, though beveled off from be- 

 hind for\vards, terminates in a blunt apex by attrition against the 

 small middle incisors of the upper jaw ; the posterior surface of the 

 crovvn is impressed -svith a narrow longitudinal groove. These in- 

 cisors, likę those above, are developed by a temporary pulp, and have 

 the fang contracted and solidilied. In this respect the Koala re- 

 sembles the Phalangers, and difFers from the Potoroos, Avhich have 

 the fang of the large anterior incisors open for the reception of a 

 persistent pulp. In the compressed and sectorial stnicture of the 

 preemolares of the Koala, \ve perceive, however, an evident transition 

 to the characteristic form of these teeth in Hypsiprymnus ; but in 

 this genus the preemolares are still more compressed, and are remark- 



