466 Bulletin American Museum of Natural History. [Vol. XXXIV, 
molars although other features indicate that they are more probably Insec- 
tivora. 7 
In absence of satisfactory evidence I have made only such changes in 
the accepted arrangement as seem sufficiently well founded to be permanent. 
_ The reference of the Apatemyide and Mixodectidee to the Insectivora 
rather than to the Primates has been discussed by Matthew in 1909. No 
conclusive evidence as to the affinities of either of these groups has been 
furnished by the new material from the Lower Eocene. Such additional 
data as are at hand tend to emphasize the affinities of both to the Eocene 
Tarsiidse, whose reference to the Primates rests upon very strong evidence.* 
The affinities of all these Eocene Primate and near-Primate groups will 
be re-examined and the evidence evaluated by my colleague Dr. Gregory, 
to whose able and judicial consideration I leave the question, observing 
that the retention of the two families in the more generalized and primitive 
group Insectivora seems advisable until adequate evidence is at hand of 
their belonging to the more specialized and progressive group Primates. 
MIXODECTID:. 
The reference of Cynodontomys and Microsyops to this family appears 
to be open to serious doubt. The lower molars are unquestionably much 
like those of Mixodectes, but there the resemblance ends. The upper molars 
are by no means so close; the premolars are of wholly different type, and 
the homologies of the enlarged front teeth may not be the same. In Mizo- 
dectes the three premolars are preceded by a canine, recognizable by its 
larger size than pe and more external position; and in front of this is the 
enlarged spatulate tooth which must therefore be an incisor. In Micro- 
syops there are apparently three premolars decreasing progressively forward, 
and the tooth in front of them may be either an incisor or a canine. In the 
upper jaw of Indrodon, a near relative of Mixodectes, there are three pre- 
molars, progressively smaller forward, a moderately large one-rooted canine 
in front of them, and two incisors, the more median one enlarged. In the 
upper jaw of Microsyops there are three premolars progressively smaller 
forward, and front of them and just behind the maxillo-premaxillary suture 
is a two-rooted canine, a little larger than p? and more externally set; the 
premaxilla is unknown but must have had an enlarged incisor to correspond 
to the enlarged lower tooth. P¥ of Mixodectes is a peculiarly specialized 
tooth, the principal cusp high, stout, simple and somewhat recurved. In 
1 Although it is far from certain that all of the Eocene genera referred to this family 
are Primates. 
