298 PATAGONIAN EXPEDITIONS! PAL/EONTOLOGY. 
lata , with the suborders, 1 Condylarthra, 2 Litopterna, 3 Perissodactyla, 4 
Artiodactyla, 5 Amblypoda: II Notoungulata , with the suborders, 1 Typo- 
theria, 2 Toxodontia, 3 Entelonychia, 4 Astrapotherioidea, 5 Pyrotheria: 
III Subungulata , with the suborders, 1 Embrithopoda, 2 Hyracoidea, 3 
Proboscidea, 4 Sirenia. Except for the position assigned to the Litop- 
terna, this scheme, so far as it deals with South American forms, is sub- 
stantially the same as that of Gregory and Lydekker, with whose general 
views I am disposed to agree. 
Leaving aside for the present the imperfectly known Pyrotheria and 
Astrapotheria, the indigenous South American groups of hoofed animals 
are, in my judgment, all more closely interrelated than they are to any 
of the northern orders, which is substantially the conclusion reached by 
Lydekker. That the toxodonts, typotheres and homalodontotheres together 
form a natural assemblage of allied forms is a matter of practically uni- 
versal agreement ; it is the position of the Litopterna that gives rise to the 
greatest difference of opinion. My own views on this question and the 
reasons for them are fully explained in Vol. VII of these Reports. 
The four groups, whatever rank be assigned to them, agree in the fol- 
lowing significant particulars : (1) Though some of the incisors may be 
enlarged and tusk-like, there is a gradual transition in form from the inci- 
sors to the grinding teeth, except in the Proterotheriidae. (2) The premo- 
lars are different from the molars. (3) The grinding teeth are lophodont. 
(4) In the upper molars the posterior crest is short and more or less imper- 
fectly developed. (5) The lower molars are bicrescentic and, except in 
the Litopterna, the anterior crescent is much smaller than the posterior. 
(6) A pillar, or spur, is present in the inner valley of the posterior crescent 
this has been secondarily lost in a few of the proterotheres. (7) 
rarely has a talon and it is never large. (8) The odontoid process of the 
axis is always conical, even in the long-necked forms. (9) The scapula 
frequently has two prominent metacromia. (10) The ulna and radius are 
always separate, except in the later Macrauchenidae. (11) Save in the 
latest toxodonts, the femur retains the third trochanter. (12) The carpal 
bones are arranged in alternating series and there is no free central. (13) 
The number of digits in manus and pes ranges from five to one and the 
symmetry is usually mesaxonic ; digital reduction is “ inadaptive” in char- 
acter. (14) The astragalus has a narrow trochlea and convex head, which 
articulates only with the navicular and is far removed from the short 
