p 
698 The American Naturalist. [August, 
The families of this order are the following : 
Incisors present in normal number; canines pres- 
ent; molars numerous, rooted, and enamel- 
covered ; Prorastomide. 
Incisors, in less than normal number ; no canines ; 
molars in normal number, rooted, and enamel- 
covered ; Halitheride. 
No incisors; molars present, covered with enamel, 
and in increased number ; Manatide. 
Incisors present; molars prismatic, without enamel, 
and in reduced number ; Halıcoride. 
Teeth none ; Rhytinide. 
The ProrAstomip# includes but the one genus, Proras- 
tomus Owen, and this the single species P. sirenoides Owen. 
This is a highly interesting form, having a dentition inter- 
mediate between that characteristic of other members of the 
order and the typical mammalian formula. This is especially 
true in the normally constituted incisor and canine teeth. The 
molars are, like those of the manatees, cross-crested grinders, 
and in larger number than that normal to mammalia generally. 
The single species has been found in beds of uncertain but 
probably Eocene age in the West Indian Island of Jamaica. 
The greater number of extinct Sirenia belong to the HALI- 
THERIIDE, and they occur alike in the old world and in the new. 
The genera are as follows: 
Incisors 3; molars?; Dioplotherium Cope. 
Incisors 4; molars 6 or 7, the last superior . 
the most complex; symphysis decurved, com- 
pressed ; Halitherium Kaup. 
Incisors 1; premolars, 3; molars, 4, the last 
superior reduced, simple ; Miosiren Dollo. 
Incisors i; molars?; symphysis long, not de- 
curved, cylindric; Anoplonassa Cope. 
The incisors in the first three genera are tusk-like; in the last 
they are in the lower jaw, with short root, and are easily shed. 
Six or seven species of Halitherium are known from the Miocene 
and Pliocene beds of Western and Southern Europe. The 
