BY W. H. TWBLVETREES AND W. F. PETTERD. 29 



The articular surfaces of both ends are abraded, exposing 

 uniformly cancellous structure of the osseous substance. 

 A transverse section of the shaft shews a loose cancellous 

 character all through : the cancelli are coarser towards the 

 centre, but there is no medullary cavity as in the Onomo- 

 dontia, Dinosauria, and other extinct reptilia, nor is there 

 any differentiation into peripheral bony wall and spongy 

 cancellated centre, as in some Permian reptiles. It is true,. 

 Prof. Owen refers to a femur of Rhombopholis scutulatus 

 as being hollow,* but it is not certain that Rhombopholis 

 was labyrinthodont.t Indeed, verj' few limb bones of 

 labyrinthodont amphibia have been determined : a glance 

 at the annexed list shews that the si3ecies and genera of 

 the order have been always founded on vertebrte, jaivs and 

 other parts of the skull. Hence, in discoveries of isolated 

 bones as those under review, caution is needed in drawing 

 conclusions. 



Under the microscope the larger cancelli are seen to be 

 filled with opaque earthy material. They are sigmoid, ellip- 

 tical, branched and otherwise irregular in shape, and often 

 contain grains of quartz derived from the sandstone and 

 confirming the authenticity of the specimen. The osseous 

 substance surrounding the cancelli is sprinkled with 

 ellipsoidal and fusiform cells onl}" faintlj- and occasionally 

 discernible in the slide. These are, doubtless, bone 

 lacunas, masked by the balsam of the mount. 



The only conclusion which can be legitimately drawn 

 from the form and structure of these humeri seems to be 

 that they belonged to amphibian vertebrates. Although 

 any more definite reference is impossible at present, it,, 

 nevertheless, appears to us desirable to place these remains 

 on record, and thus render them available for comparison 

 with future discoveries. 



* Owen. Palseontology, 1861, p. 215. 



f On the remains of Labyrintiodonts from the sandstone of Warwick 

 L. Miall. 2 J. Geol. Soc. 187i, p. 433. 



EXPLANATION OF PLATE. 



Fig. 1. -Humeru.s of labyrinthodont amphibian from Lower 

 Mesozoic sandstone, Tasmania. British Museum cast. 

 Anconal (back) asj^ect. Nat. size. 



Fig. 2. — Ditto, ditto. Thenal (front) aspect. Ditto. 



Fig. 3. — Humerus from Domain sandstone quarry. Hobart : 

 Lower Mesozoic. Thenal (front) aspect. Nat. size. 



Fig. 4. — Microscopical section of shaft of humerus, Nos. 2 and|3,. 

 showing: cancellous structure of bone, x 10. 



