MAY, 1921. AMERICAN MARSUPIAL, C^NOLESTES OSGOOD. 85 



The first has a much broader and heavier transverse process, the whole 

 lateral surface of which is firmly attached to the ileum. The condition 

 is much like that in Phascologale, Sminthopsis, Philander, and Myrme- 

 cobius. A slightly greater proportion of the second sacral touches the 

 ileum in Marmosa, Peramys, Dasyurus and Perameles; a still greater in 

 Didelphis, Phascolarctos and Phascolomys; and in Trichosurus, Petaurus, 

 Petrogale and Macropus the second vertebra is almost or quite as fully 

 attached as the first; while in a single specimen of Thylacinus, the second 

 sacral, although heavily ankylosed to the first, does not reach the ileum 

 at all. The two sacrals are ankylosed to each other laterally, but a large 

 perforation persists between their transverse processes. Their general 

 character corresponds closely with that of the last lumbar, the chief 

 differences being in their widened and more horizontal transverse 

 processes and in the greatly compressed zygapophyses, both anterior 

 and posterior in the case of the second, and mainly the postzygapophysis 

 in the case of the first. The first has a well-developed and forwardly 

 directed spinous process similar to that of the last lumbar. The second 

 has a smaller, more pointed spinous process directed slightly backward. 



The first caudal and sometimes the second is ankylosed to its 

 predecessor by a narrow bony strip stretching between the extremities 

 of the transverse processes. The first and second are essentially similar 

 to the sacrals except that they have no traces of spinous processes and 

 that the zygapophyses are expanded slightly in the first and greatly in 

 the second, with short rounded metapophyses. The third and fourth 

 caudals are similar to the second but their transverse processes are 

 inclined forward and the first chevron bone is found over their inter- 

 vertebral space. The fifth caudal is the first to lack the neural canal and 

 postzygapophyses, but the transverse process is still undivided, although 

 somewhat reduced in lateral extent and lengthened antero-posteriorly. 

 In some specimens this transverse process is distinctly emarginate 

 laterally. The sixth caudal is elongate and subcylindrical with rather 

 prominent metapophyses and short crescentic anterior and posterior 

 transverse processes. The succeeding vertebrae are almost exactly 

 similar up to the sixteenth which has only the merest traces of processes. 

 The remainder taper gradually to a very slender tip, the total number of 

 caudals being twenty-seven. The ninth and tenth are the longest of the 

 caudals each measuring about 7.7 mm. Nineteen chevron bones are 

 present from the third to the twenty-second caudals. These have one to 

 four longitudinal ridges on their under surfaces which give them a fluted 

 appearance. They are nearly as wide as the bodies of the vertebrae. 



The characters of the caudals are of course of little or no significance 

 in the indication of relationships, but it is of some interest to note that 



