SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 419 



Thomas (1895, p. 872) states that in Ccenolestes both feet are penta- 

 dactyl. On the fore foot the pollex and fifth toe are provided with dis- 

 tinct nails and the remaining toes with well developed curved claws. 

 The third digit is the longest ; the second and fifth subequal and shorter. 

 The hind foot is non-syndactylous and not modified into a hand, as it is in 

 the opossums. The hallux is short, clawless and not properly opposablc, 

 developed much as in Phascogale wallacei. The remaining digits of the 

 hind foot are subequal, the fourth slightly the longest, and all provided 

 with claws. 



CsENOLESTINsE. 

 HALMARHIPHUS Ameghino. 



(Plate LXIII, Figs. 9, ga ; Text Fig. 7.) 



Halmarhiphus Amegh. ; Revista Argent., Hist. Nat, T. I, p. 308, 1891. 



This genus is peculiar in combining characters of both marsupial sub- 

 orders. The tuberculo-sectorial 'molars are structurally the same as in 

 Microbiotherium or Didelphys and the antemolar formula is that of the 

 Polyprotodontia, while in the anterior portion of the mandible Diproto- 

 dont features are apparent in the enlargement of the median incisor and 

 the vestigial character of the remaining incisors, canine and anterior pre- 

 molar. Halmarhiphus is of exceptional interest, not only as the direct 

 ancestor of Ccenolestes, but as a constructive stage in the evolution of the 

 Diprotodontia. This will be treated at greater length in the discussion 

 of the relationships of the Caenolestidae. 



' Ameghino (1894, pp. 96-103; 1903, p. 159) places Halmarhiphus md. 

 Garzonia in the family Garzonidae. It appears preferable, however, to 

 group them with Ccenolestes as a subfamily of the Caenolestidae, to which 

 they unquestionably belong. This subfamily has been named the Caeno- 

 lestinae after its best known representative. 



Halmarhiphus is represented in the collection of the American Museum 

 of Natural History by the right ramus of a lower jaw (No. 9593 American 

 Museum) agreeing in size with H. nanus Ameghino. The tip of the 

 median incisor has been broken off and the first two vestigial teeth shed 

 from their alveoli. Otherwise the dentition is complete and unworn. 



Nothing is known of the upper teeth. The lower dental formula may 

 be written T, T, ^, T, if definite homologies are assigned to the vestigial 



