416 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



DIPROTODONTIA. 



CsENOLESTIDsE. 



(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 Ccznolestes (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 Pakeoihenies (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 nudnm, 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 Epanorthiis. 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: C^ENOLESTIDAi. Pes, so far as known (Canolestes), non-syndactylous. Sec- 

 torials, when present, restricted to the posterior premolar above and the first molar 

 below. Superior premolars three in number (Palceothentes, C&nolestes), 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 : C&NOLESTINsE. Dental formula Aj^, i (Ccenolestes). Sectorials not 

 developed. First and second superior molars fully quadritubercular, third and fourth tri- 



