282 LLOYD’S NATURAL HISTORY. 
molar teeth carrying two or three longitudinal ridges support- 
ing numerous small tubercles, such ridges being separated by 
deep grooves, as shown in the accompanying figures, and the 
number of ridges in the upper molars being usually one in 
excess of those of the corresponding lower teeth. As in the 
Diprotodont Marsupials, there is a single pair of large and 
sharp incisor teeth in the lower jaw; and a further superficial 
resemblance to that group is often shown by the last premolar 
being modified into a large compressed and cutting tooth with 
well-defined parallel groovings and ridges on the sides of its 
crown. 
The numerous genera of the Multituberculata are arranged 
under several families, which will form the headings under 
which our brief remarks will be arranged. 
FAMILY TRITYLODONTID~. 
GENUS TRITYLODON. 
Tritylodon, Owen, Quart. Journ. Geol. Soc., vol. xl., p. 146 
(1884) ; Lydekker, Cat. Foss. Mamm. Brit. Mus., pt. v., 
p. 208 (1887). 
In this family the upper molar teeth have three longitudinal 
ridges, as shown in the last illustration, and are broader 
than long; while the premolars are of the same general struc- 
ture, but somewhat simpler. In the upper jaw there is one 
pair of large, somewhat chisel-like incisors, followed by a 
second very small and functional pair; then, owing to the 
absence of a canine, comes a very long gap, followed by the 
two premolars, and these again, by the four molars. The lower 
jaw is unknown. 
This genus is typically represented by Z: Zongevus, from the 
Secondary rocks of South Africa, which was an animal of the 
