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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Nov. 21, 



The bones are all in the same, and that a very peculiar, mineral 

 condition — the Haversian canals being for the most part filled up 

 with threads of native copper ; so that the fossils are not only ex- 

 ceedingly dense, but, in consequence of their internal flexible me- 

 tallic support, their thinner and more delicate parts bend, rather than 

 break, when force is applied to them. 



The characters of the cervical vertebra and of the astragalus, which 

 are fortunately the best-preserved of all the fossils, at once demon- 

 strated the remains to belong to the genus Macrauchenia (Owen), 

 while the entire absence of epiphysial sutures in the vertebrae and 

 the long bones, and of similar indications of immaturity in the frag- 

 ment of the skull, proved the animal to have attained its adult con- 

 dition. The vertebra and the astragalus, however, have not more 

 than half the size of the corresponding bones of the species, M. Pa- 

 tachonica, discovered by Mr. Darwin, and described by Professor Owen 

 in the ' Appendix to the Voyage of the Beagle and as, in addition, 

 these and the other bones present different proportions from those of 

 the Patagonian species, I have no hesitation in regarding the fossils 

 collected by Mr. Forbes as the remains of a distinct species, for which 

 I propose the name of Macrauchenia Boliviensis. It will be con- 

 venient to commence the description of these fossils with those parts 

 upon which the diagnosis of the species may be most safely rested, 

 viz. the cervical vertebra and the astragalus. 



The cervical vertebra (Plate VI. fig. 1). — The great length of the 

 centrum of this vertebra, the peculiar form of its transverse processes, 

 and the absence of perforations for the vertebral arteries in them 

 are characters which, in the present state of knowledge, oblige the 

 anatomist at once to refer it either to one of the existing Camelidce 

 or to the genus Macrauchenia ; while the two strong, converging 

 ridges which mark the posterior half of the under surface of the ver- 

 tebra, and meet to form a single ridge, which dies away anteriorly in 

 the middle of that surface, togetherwith the slight concavity of both the 

 posterior and the anterior articular faces of the centrum, are decisive 

 in favour of the latter alternative. In fact, the excellent description 

 of the cervical vertebras of Macrauchenia Patachonica which has been 

 given by Professor Owen applies so well to that of M. Boliviensis, 

 that, referring to the paper in the ' Appendix to the Voyage of the 

 Beagle,' already cited, for a general account of the characters of 

 Macrauchenian vertebrae, I shall content myself with pointing out 

 the resemblances and differences of the Bolivian from the Patagonian 

 Macrauchenia, and from the existing Auchenioz. The dimensions of 

 the centrum of the cervical vertebrae of the two Macrauchenia;, and 

 of the fourth cervical of a Guanaco and of a Vicugna in the College of 

 Surgeons' Museum are as follows : — 



M. Boliviensis. 



M. Patachonica. 



Guanaco. 



Vicugna. 



in. 



in. 



in. 



in. 



Length 3-8 



Width of anterior face 1*1 

 "Width of posterior f aoe 1-25 



6-6 

 3-2 

 3-4 



4-6 

 1-1 

 1-3 



4-0 

 •8 

 1-0 



