1890.] The Extinct Sirena. 701 
Fossil HALIcoRID are unknown, except some bones of very 
FIG. 3.—Manatus americanus Cuv.; skull one-twelfth natural size; from Cuvier. * 
ight side; 2, from above. a, Premaxillary bone; 5, foramen infrantitole; c, m. £ 
d, frontal; e, molar; /, ieee process of EEE g, parietal 
late Tertiary age found in Australia. In the genus the 
dental formula is I. 1; C. $; M. 3, and the molars are prismatic 
and of cylindric or oval capes. as in some Edentata. (Plate 
XXVI) The Ruytinips# are represented thus far by the typical 
genus and species only, the R. gigas Zimm., which dwelt on 
the coasts of Behring Sea up to a late period of human history. 
It is one of the large species of mammalia exterminated by man, 
and its bones are found in considerable abundance on Behring's 
Island, Commander's Island, etc. Nearly complete skeletons are 
