483 



§ 26. Procoptodon Bapha (Characters of Mandible and lower Incisor). — The detec- 

 tion of the crown of the premolar in the formative cavity of a fragment of the mandible 

 (Plate XC. figs. 8-12) of an immature Macropod, with the indication which the pro- 

 portions of that fragment yielded of its Procoptodont character, led to a reference of 

 such fragment to the genus and species represented by the plaster cast of a mutilated 

 mandibular ramus with the molar series of teeth figured in Plate XCIIL, the original 

 of which is in the Museum of Natural History, Sydney, New South Wales. 



This ramus was of a mature and somewhat aged individual ; the molar series shows 

 wear even to the hindmost grinder ; the premolar is ground down to the stump, but it 

 enabled a comparison to be made with that in the young specimen (p. 457) ; and the 

 conformable relation of size of the succeeding molars with that exemplified between 

 the premolar and molars of Procoptodon Pusio and Procoptodon Goliah seemed to 

 support a conclusion as to a species of intermediate bulk, for which the name Procop- 

 todon Bapha was proposed. 



Since pages 454-465 and Plates XC.-XCV. have been printed off, I have been 

 favoured by my friend Dr. George Bennett, F.L.S., with the mandible and teeth 

 forming the subject of Plate CXXVIIL, which specimen was discovered by his son, 

 George Bennett, Esq., in the drift deposits of one of the creeks in Darling Downs. 



Sufficient of the worn premolar (Plate CXXVIIL p z) in this mandible remains to 

 show its identity, in antero-posterior and transverse dimensions of the crown, with that 

 in the type-subject of figs. 8 & 10 of Plate XC. The agreement in size of the 

 succeeding molars with those of the cast figured in Plate XCIIL is also specific. 

 The additional characters, therefore, yielded by the specimen under view are those of 

 Procoptodon Bapha. 



I may first note the deep depression (Plate CXXVIIL figs. 3 & 4, a) behind the 

 roughly sculptured symphysial surface (s) in each ramus. This depression is just below 

 the middle of the long diameter of that surface ; its aperture is elliptical, with the long 

 axis (of 8 lines) in the same direction ; it extends forward half an inch into the sub- 

 stance of the jaw, ending in a point. The depth of this postsymphysial depression was 

 obscured in the cast described at p. 459. Phascolomys has also the pair of depressions, 

 as seen in the entire mandible at the back of the symphysis, but of smaller relative size 

 and rounder shape : Macropus has not this character. 



Above the symphysial surface in Procoptodon Bapha a low longitudinal ridge bounds 

 above a shallow longitudinal channel (fig. 4, b). 



The alveolus (ib. c) of the incisor is 1^ inch in depth, 6 lines in antero-posterior 

 diameter, 4 lines in transverse diameter near the outlet ; the socket decreases slightly 

 in both diameters to the bottom. The direction of the socket inclines more forward 

 than does the long axis of the symphysis. The size and position of the outlet of the 

 dental canal (figs. 1 & 3, v) is the same as in the cast (Plate XCIIL fig. 1, v). 



The enamelled crown of the lower incisor (figs. 1 & 3, i) is less, especially in fore-and- 

 aft diameter, than the root ; it is also relatively much shorter and thicker than in 



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