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THE 
AMERICAN NATURALIST 
Vor. XXIV. AUGUST, 189o. 284. 
THE EXTINCT SIRENIA. 
BY E. D. COPE. 
T HE Sirenia occupy an especial place in the mammalian econ- 
omy, which is only shared by the seals. They are denizens 
of the coasts of the sea and its branches, and of the larger rivers. 
Their present distribution differs from that of the seals in that it 
especially includes the tropics, where seals are rare; and excludes 
the polar regions, where seals abound. Extinct forms occur, 
however, in all the northern temperate regions that have been 
explored, and there is no reason to doubt that the order was of 
world-wide distribution during the early and middle parts of 
Czenozoic time. 
The derivation of the Sirenia is shrouded in mystery. They 
have evidently diverged from land mammals of primitive placental 
type, and have become specialized in accordance with their 
peculiar modes of life, and have in many respects degenerated. 
Rudiments of pelvis and posterior limbs are present in most of 
them, and they are especially large in some species of the extinct 
genus Halitherium. Part of such a pelvis from South Carolina 
is represented in Plate XXV, Fig. 6. The dentition has become 
more and more reduced, till the enamel layer is lost in Halicore, 
and the teeth have all disappeared in Rhytina. The least gen- 
eralized form is Prorastomus Owen, of which remains of a single 
species (P. sirenoides) have been found in the late Cenozoic beds 
of certain islands of the West Indies. Here the dentition is 
stated by Lydekker to be: 1.3; C.¢; M. $?. 
