1910.] Interrelations of Patagonian Ungulaten. 383 



Proboscidea, Amblypoda, etc., and have been derived independently of these 

 but from the same ancestral order of protungulates, it follows that the num- 

 erous resemblances in special characters between southern and northern 

 forms are due to similar adaptations occurring in the divergent descendants 

 of similar and more closely related ancestors. This confusing mixture of 

 homological and analogical resemblances deprives of permanent value all 

 attempted classifications and ])hylogenetic conclusions which are based 

 upon isolated points of resemblance between northern and southern groups, 

 in respect either to the dentition or to the feet. 



Summary. 



The foregoing views on the interrelationships of the extinct South 

 American ungidates are summarized in the subjoined table, which is doubt- 

 less very imperfect, since it deals only with the better known forms; but it 

 may, perhaps, serve as a trial hypothesis. 



I. Order Protungulata (Condylarthra). Upper molars bunodont, 



sexitubercular, with mesostyle. Paracone and metacone rounded 

 externally. Astragalus and calcaneum, so far as known, approximating 

 to the Euprotogonia (Phenacodont) type. 



1. Quadrangular arrangement, hypocone very prominent, e. g., Di- 

 doJodus, Notoprotogonia. ( ?Condylarthra). 



2. Triangular arrangement, hypocone and protostyle subequal, e. g., 



Guiliebno flower ia, Ricardolydekkeria ( ?Taligrada, i. e., Peripty- 

 chidse or Pantolambdidte.) 



II. Order Notoungulata. Upper molars when known more or less 

 rhinocerotic: i. e., progressively hypsodont, wath flattened ectoloph, 

 a long protoloph, smaller metaloph, a crista, proto- and hypostyles, 

 no mesostyle. Lower molars with talonid typically much longer than 

 trigonid. Carpus (when known) alternating (?'. e., lunar touching unci- 

 form). Structure of limbs and feet various. 



1. Suborder Homalodotheria. Astragalus (Homahdotherium) re- 

 taining distinct neck and rounded head, trochlea flattened not 

 compressed; digits {Homahdotherium) 5-5. Complete Placental 

 dentition (|x"o) ^^ typical forms. Incisors and canines (when 

 known) subequal. 



?a. Size small; molars brachyodont; protoloph well developed, 

 metaloj)h beginning, hypocone prominent, e. g., Henricosbor- 

 nia. (Referred by Ameghino to the Lemuroidea.) 

 W. Size medium; molars subhypsodont, roundly trigonal, ecto- 

 loph flat, rather straight, protoloph prominent. Astragalus 



