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PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
of Theosodon, a genus of Santa Cruz Litopterna, was not yet known ; in 
this animal the transition in the form of the teeth, from the first incisor to 
the last molar, is even more regular and gradual than it is in Homalo- 
dontotherium. 
The teeth are of nearly even height, except that in some individuals, 
probably males, the canines project above and below the level of the lower 
and upper series respectively. Roots are formed at an early stage of 
tooth-development, but the crowns are relatively high, though I cannot 
follow Flower in calling them “ hypsodont,” a term which should be 
reserved for the prismatic tooth, which develops roots only in advanced 
age. 
A. Upper Jaw (Pis. XXVIII, figs. 1, 2; XXIX, figs. 2, 3). — The two 
straight and slightly divergent dental series are connected in front by the 
short and moderately curved, transverse row of incisors. These teeth 
are quite simple and conical, increasing somewhat in size from i- to i- 
and have very strongly developed cingula, both internal and external. 
The first incisor, r 1 , has a long, bluntly pointed crown, with a median 
vertical thickening, thinning to an edge on each border. The crowns of 
i- and -, when viewed from below, have an acutely pointed, hastate shape, 
broadening abruptly from the root. The median thickening produces 
quite a distinct convexity upon the external face of the tooth and the 
edges are trenchant. I- is considerably broader than i-, but otherwise of 
similar shape ; it has, sometimes at least, a small internal cusp arising 
from the cingulum. 
The canine differs considerably in the various individuals in relative 
size and prominence. Presumably, this is a sexual rather than a specific 
character, but the materials are insufficient for a definite determination of 
this question. In Flower’s specimen, the type of H. cunninghami, the 
canine “only differs from the posterior incisor in being somewhat larger 
and in trifling details of configuration. The apex is rather more pointed 
and conical, being supported by a median vertical ridge, not only on the 
outer, but also on the concave inner surface of the crown ; the inner 
tubercle is relatively smaller to the principal cusp ” (Flower, loc. cit., 
P . 176). 
In his original description of H. segovice, Ameghino distinguishes this 
species from H. cunninghami , among other characteristics, by “the largely 
developed upper canine” (’91, 295). Much more probably, however, this 
