142 BULLETIN 16 9, UNITED STATES NATIONAL MUSEUM 



correct. The only taxonomic change to be introduced is that a fifth 

 genus is made to receive a species that Gidley placed doubtfully in 

 Palaechthon. 



Family ?ANAPTOMORPHIDAE Cope, 1883 



In this fauna the three genera Paromomys, Palaechthon, and 

 Palenochtha are very tentatively listed with the Anaptomorphidae, 

 although (as will appear) the relationship is not clear and tliis whole 

 complex of early primates is highly polyphyletic and very confusing. 



Paromomys, Palaechthon, and Palenochtha evidently belong to 

 slightly divergent lines, but they have certain characters in common. 

 The most important of these are: 



1. An enlarged, semiprocumbent lower incisor, its root not extending beneath P^. 



2. Other lower incisors vestigial and variable or absent. 



3. Lower canine present and only slightly reduced. 



4. Pi and probably sometimes P2 absent.^^ 



5. P4 little or not enlarged, trigonid simple, elevated, with low, 2-cusped talonid. 



6. Molar trigonids with small, generally short and quadrate basins, paraconids 

 generally distinct but reduced, cusps marginal or nearly so. 



7. Heels of Mi_2 large, simple, broadly basined. 



8. M3 with third lobe, which, however, differs greatly and characteristically in 

 the three genera. 



9. P^ (as far as known) 2-rooted and not transverse. 



10. P^ transverse, strong protocone, paracone and metacone little or not differ- 

 entiated, conule feeble or absent. 



11. Upper molars without mesostyle, protostyle, or hypocone; two small but 

 distinct conules; posterointernal corner of crown expanded and basined to varying 

 degrees; inner face of molar with vertical groove at least on IVP. 



These suggest a possible fairly immediate common origin for the 

 three genera, but they are diverging from each other, principally as 

 follows: 



Paromomys: Antemolar dentition of unmodified basic type as listed above- 

 Molar trigonids very short and quadrate, paraconid almost disappearing by fusion 

 with metaconid on M2-3. Third lobe of M3 very strong, with at least two distinct 

 cusps. Inner base of M^, at least, more or less bilobed. Posterointernal expan- 

 sion of upper molars very marked. 



Palaechthon: P4 more progressive, with distinct paraconid and metaconid. 

 Molar trigonids less quadrate and paraconids more distinct. Third lobe of M3 

 weaker but still with two cusps. Upper molars not bilobed, posterointernal expan- 

 sion less. 



Palenochtha: Anterior dentition further modified by loss of another tooth, prob- 

 ably P2. P4 much as in Paromomys. M3 with weak, 1-cusped third lobe. Upper 

 molars not bilobed, posterointernal expansion slight. 



Except for the absence of P2 (which, however, is not absolutely cer- 

 tain), Palenochtha seems definitely the most primitive of the three and 

 its general structure is such as might be expected in the ancestry of 



58 Certain homologies, discussed on a later pa!;e, are here assumed. Exact identification is impossible, but 

 as the teeth are probably homologous between the genera in question, if they are labeled consistently it does 

 not matte from the point of view of determining affinities whether the labels prove to be correct or not. 



