SYSTEMATIC ARRANGEMENT 29 
NOTUNGULATA 
Order 1. Upper molars composed of an external longi- 
tudinal crest and two transverse crests, the posterior the 
less developed; lower molars composed of two joining cres- 
cents with a “‘pillar’’ in the posterior crescent; structure 
of the feet and limbs varying. 
Suborder 1. Litopterna: teeth brachydont to hypsodont; 
lower molars with the anterior and posterior cres- 
cents subequal; squamoso-periotic region not in- 
flated; limbs elongated; pes unguligrade; digits 3-3 
or I-I, 
Suborder 2. Typotheria: teeth hypsodont lower molars 
with the anterior crescent shorter than the poste- 
rior; squamoso-periotic region inflated; limbs 
elongated in varying degrees; pes plantigrade to 
semi-plantigrade; digits 5-4 or 4-4. 
Suborder 3. Toxodontia: teeth brachydont to hypso- 
dont; lower molars with the anterior crescent shorter 
than the posterior; squamoso-periotic region in- 
flated; limbs short; pes semidigitigrade to digiti- 
grade; digits 3-3. 
Suborder 4. Homolodontotheria: teeth brachydont; 
lower molars similar to those of Toxodontia; limbs 
moderately elongate; pes semidigitigrade; digits 
with large curved claws, 5-5. 
Suborder 5. Astrapotheria: teeth brachydont to mod- 
erately hypsodont; canines enlarged into tushes; 
molars similar to those of Toxodontia; limbs greatly 
elongated; feet unknown. 
PROBOSCIDEA 
Order II. (see page 68) 
Suborder 1. Pyrotheria: incisors developed into tushes; 
molars bilophodont; limbs short, especially the 
lower element; feet digitigrade. 
