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PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
DIPROTODONTIA. 
CrENOLES TIDAi. 
(Plates LXIII, LXIV; Text Figs. 7-9.) 
All the Santa Cruz diprotodonts may be included in one family, of 
which a single survivor remains in Ccenolestes (PI. LXIII, figs. 14-14$). 
The species are small, possibly owing to competition with the placental 
herbivores acting as a check on adaptive radiation. 
Before proceeding to a discussion of the group, it is desirable to offer 
some explanation of the classification adopted. Ameghino in his latest 
publication on the Diprotodontia (1903, p. 159) recognizes three families 
among the Santa Cruz representatives of the suborder : the Abderitidae, 
Epanorthidae and Garzonidae. These have been referred to in a general 
way by other writers (Thomas, 1895 ; Bensley, 1903) as the Epanorthidae. 
The genus Epanorthus was proposed by Ameghino in 1889 (1889, p. 271) 
as a substitute for Palceothentes (Moreno) Ameghino (1887, p. 5), on the 
assumption that the latter conflicted with Palceoteuthis, a genus of ceph- 
alopods. Although Moreno’s Palceothentes (also spelled by him Palce- 
otenthes ) is a nomen nudum , the description published by Ameghino in 
1887 gave this term a priority in nomenclature from which he was not at 
liberty to depart by the substitution of Epanorthus. The latter name can 
no longer be retained either for a genus or to designate a family. The 
writer prefers to group all the Santa Cruz diprotodont marsupials in a 
single family, which may be called the Ccenolestidce (Trouessart, 1898, p. 
1205) from its only surviving and best known representative Ccenolestes. 
Family: CAIN OLES TIDAi. — Pes, so far as known ( Ccenolestes ), non-syndactylous. Sec- 
torials, when present, restricted to the posterior premolar above and the first molar 
below. Superior premolars three in number {Palceothentes, Ccenolestes ), the anterior and 
median small, the posterior large and trenchant. Functional lower premolars 2-none. 
Vestigial teeth always present in the lower jaw. Molars rooted, brachyodont, tuberculo- 
sectorial or buno-lophodont, undergoing progressive complication in the superior series by 
the addition of a hypocone. Hypertrophied lower incisors lanceolate with cutting edges 
enamel layer confined to the outer face. 
First Subfamily : CAIN 0 LEST IN AS. — Dental formula - LL L. ~ {Ccenolestes). Sectorials not 
developed. First and second superior molars fully quadritubercular, third and fourth tri- 
