FISHES—REGAN, 43 
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 precéded by a milk tooth. I have examined the skulls of Thylacinus and 
several other Dasyuridae (Fig. 7, B,C) and find that they agree in havine the orbits 
well backward, the nasal processes of the praemaxillaries long, 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 (Fie. 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 Zhylacinus, has been independently evolved. 
MToLaANtIA. 
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, J. platyceps, Owen,* from the Pleistocene of Lord Howe Island, 
and M. oweni, A. S. Woodward, from the Pleistocene of Queensland.  Niolaimia 
* Owen, Phil. Trans., 1886, pp. 471-480, pls. xxix, xxx ; and 1888, pp. 181-191, pls. xxxI—xxxvit. 
ft Woodward, Ann. Mag. Nat. Hist. (6) 1, 1888, p. 89. 
G 2 
