534 



PROFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTEALIA. 



bed in the " Melbourne district," described in my ' Catalogue of Fossils in the Museum 

 of the Eoyal College of Surgeons' (4to, 1845), p. 308, no. 1491 ; and such trace of socket 

 showed the tooth to have been implanted by two fangs. The corresponding divisions of 

 the socket of do, with the fangs in situ, are better preserved in the specimen figured in 

 Plate XLII. fig. 5, and Plate XLIII. figs. 1 & 2, d 3. Dr. Hobsojt, shortly before his 

 death in 1848, transmitted to me a sketch of this tooth in situ, in a fragment of the 

 lower jaw of a young Diprofodon (Cut, fig. 2), according to which the anterior as well 

 as the posterior lobe of 3 is in the form of a transverse I'ig- 2. 



wedge ; there is a basal ridge along both the fore and hind 

 parts of the crown, the latter being the broadest ; in short, 

 d 3 presents, in miniature, the bilophodont type of the 

 succeeding molars. From the attrition of the two lobes it 

 may be inferred that the opposing molar above was also 

 transversely two-ridged. That the tooth (fig. 2) answers 

 to the one which occupied the socket (d 3) in Plates XLI. 

 & XLII. fig. 5, is shown by correspondence of size. The 

 fore-and-aft extent of the socket in both is 9 lines, the 

 breadth of the division for the anterior fang is 4 lines, of 

 that for the posterior fang 4^ lines ; the alveolar wall ex- 

 tending transversely between the two divisions exceeds a 

 line in thickness ; each fang is subcircular at its fractured 

 end, with an indent at the side turned toward the other 

 fang, indicative of a longitudinal groove into which the 

 walls of the socket enters, giving a firmer implantation to 

 the tooth. 



In the portion of mandible (Plate XLI. & XLII. fig. 5) the penultimate molar (m 2) 

 had not risen completely into place, and the posterior lobe was barely touched by masti- 

 catory work. In the mandibular ramus (Plate XLII. fig. 2), with the last molar (m 3) 

 in place and both ridges showing wear, the two divisions of the socket of d^ are retained, 

 without trace of tooth. The fore-and-aft extent of the socket is 9 lines, that of the hind 

 fossa or division is 3^ lines, that of the front one 2^ lines, and that of the intervening 

 bar is 2^ lines at its prominent part. 



In the younger jaw the second molar (Plate XLI. figs. 1 tSc 2, 4) has both lobes of 

 the crown about half worn down ; the fore-and-aft extent of the croAvn, including the 

 anterior and posterior basal ridges, is 1 inch 6 lines. The anterior basal ridge is thickest 

 at its outer part, and here the enamel has been worn off in mastication. The flat fore 

 side of the front lobe rises 5 lines above the ridge. The abraded surface (Plate XL. 

 fig. 3, a) of this lobe is 8 lines in transverse and 4 lines in antero-posterior extent, the 

 mid prirt being increased in this direction by an outswelling of the hind surface there of 

 the lobe. The outswelling of the front slope or surface of the hind lobe is situated more 

 outwardly: the abraded surface (Plate XIj. fig. 3, b) of this lobe is narrower from before 



First lower molar, d 3, j'oung Dtjyro- 

 todon, nat. size. 



