Denkschr. Österr. Akad. Wiss., Math.-nat. Klasse 110(3): 1-68. 34 figs. 4 pls.

–Recognizes three species, supposed to be stratigraphically successive, in the Late Oligocene deposits of the Linz Basin, Austria: Halitherium pergense (Toula), n.comb., H. christoli Fitzinger, and H. abeli, n.sp. The available material of these forms and their stratigraphic contexts are described or redescribed, and they are concluded to be transitional forms between Halitherium and Metaxytherium. Bone histology of sirs. is discussed, and some apparent differences among the three species in the internal structure of the ribs are pointed out. Concludes that the terms pachyostosis and osteosclerosis are inappropriate for Tertiary sirs., and proposes instead the term "Ponderosität" to describe their bone histology, which is adapted to provide ballast for diving.