FISHES— REGAN. « 



prisms interlacing to produce a characteristic pattern in cross-section. In Thylacinus 

 and Dasyurus, on the contrary, the enamel is typically Marsupial in that it is 

 penetrated by tubules continuous with those of the dentine and has the prisms straight 

 and parallel. The two genera mentioned show a special agreement in that the tubules 

 end at some distance from the surface. Ameghino states that in the Sparassodonts not 

 only the third praemolar, but the canine and sometimes the second praemolar, have 

 deciduous predecessors. In Thylacinus, as in the other Dasyuridae, only the third 

 praemolar is preceded by a milk tooth. I have examined the skulls of Thylacinus and 

 •several other Dasyuridae (Fie-. 7, B, C) and find thai they agree in having the orbits 

 well backward, the nasal processes of the praemaxillaries lone-, the nasals but moderately 

 expanded posteriorly, the maxillary and frontal meeting in a. suture, the jugal emitting 

 a postorbital process just before its junction with the squamosal, the occipital region 

 triangular in outline, the basisphenoid foramina paired and palatal vacuities present 

 (said to be absent in some species of Phascologale). 



The Sparassodonts, as described and figured in Sinclair's admirable monograph. 

 differ in the more anterior position of the orbits, shorter nasal processes of the prae- 

 maxillaries. nasals strongly expanded posteriorly, meeting the lachrymals and separating 

 the maxillaries from the frontals, the absence of a distinct postorbital process, the 

 semicircular occipital outline, the unpaired basisphenoid foramen, and the absence of 

 palatal vacuities (Fig. 7, A). 



The dentition of Thylacinus is readily derivable from the primitive Dasyurid type 

 (Phascologale); the teeth of the Sparassodonts correspond closely to those of Thylacinus 

 in form and number, except that the metacone of the fourth upper molar is vestigial or 

 absent, whereas in Thylacinus it is well-developed. 



There appears to be no escape from the conclusion that Thylacinus is a true but 

 aberrant member of the Dasyuridae, and that it has nothing to do with the 

 Borhyaenidae, a, family well characterised by peculiarities in the skull, and in the 

 structure and perhaps in the succession of the teeth. The specialised carnivorous 

 dentition, superficially similar to that of Thylacinus, has been independently evolved. 



MlOLANIA. 



The family Miolaniidae includes some large extinct Pleurodiran Tortoises that are 

 remarkable for the development of a caudal sheath of bony rings and the presence 

 of dermal bony bosses on the head. 



There are two genera, Miolania, Owen, and Niolamia, Ameghino. The former 

 includes two species, M. platyceps, Owen,* from the Pleistocene of Lord Howe Island, 

 and .1/. oweni, A. S. "VVoodward,f from the Pleistocene of Queensland. Niolamia 



* Owen, Phil. Trans., 188G, pp. 471-480, pis. xxix, xxx ; and 1888, pp. 181-191, pis. xxxi-XXXVU. 

 | Woodward, Ann. Mag. Nat. Hist. (0) i, 1888, p. 89. 



G 2 



