62 SIRENIA. 
preponderance of the Marsupial Group in these Colonies, no 
less than ninety-three species, exclusive of nine well-marked 
varieties, belonging solely to the fauna of Australia and its out- 
lying islands, while three (Aacropus agilis, Dactylopsila trivirgata, 
and Phalanger maculatus) are common to it and the Papuasian 
or Austro-Malayan sub-regions ; the number of known Marsupials 
being but one hundred and fifty-one, with twelve recognizable 
varieties, it therefore follows that Australia possesses almost two- 
thirds of the total. 
Order I.—SIRENIA. 
Head rounded, not disproportionate in size as compared with 
the trunk, from which it is inconspicuously separated by any 
externally visible neck. Nostrils valvular, separate, placed above 
the fore part of the obtuse truncated muzzle. Hyes very small, 
with a well developed nictitating membrane. Har without pinna. 
Mouth small or moderate, with tumid lips beset with stiff bristles. 
General form of body depressed and fusiform. No dorsal fin. 
Tail flattened and horizontaly expanded. Fore limbs paddle- 
shaped, the digits enveloped in a common cutaneous covering. 
No trace of hind limbs. Skin wrinkled, rugose, naked, or with 
fine hairs sparsely scattered over it. Clavicles absent. Pelvis 
rudimentary. 
The Sirenians are inhabitants of bays, estuaries, lagoons, and 
large rivers, in the shallow waters of which they find abundance 
of the marine algz and fresh-water grasses on which entirely they 
feed. They are asa rule gregarious, are slow and inactive in 
their movements, and in disposition mild, inoffensive, and 
apparently without much intelligence, for which latter reason they 
are within a measurable distance of total extinction, being valu- 
able for their flesh as food, and for their hides, but especially for 
the excellent oil which is extracted from the thick layer of fat 
immediately underlying the cuticle, as a fact they are already 
becoming very scarce and difficult to obtain in all settled districts. 
Members of the two existing genera, Manatus and Halicore, are 
natives of the tropical shores of Kastern America and the West 
Indies, Africa, Asia, and Australia, but the genus Rhytina, from 
Behring Straits, a much larger animal than either of the others, is 
supposed to have been exterminated through the agency of man 
within the last hundred and twenty-three years, but it is reported 
(Nordenskiéld, Voyage of the Vega) to have been seen in its 
original home so late as 1854. 
During the Miocene and early Pliocene epochs Sirenians 
abounded in the coastal waters of Europe and North America, 
and a species has also been discovered in the nummulitic limestone 
of the Mokattam Hills near Cairo. 
