24 Wortman— Studies of Eocene Mammalia in the 



he were to take into consideration the clawed condition of all 

 the digits. The habits of the marmosets, while as strictly and 

 completely arboreal as in any of the Primates, resemble those 

 of the squirrels more than those of the monkeys proper. Accord- 

 ing to Bates, who had excellent opportunities for observing 

 them in their native forests, the Negro Tamarin (Midas ursu- 

 lus) confines itself mostly to the larger branches, and is fre- 

 quently seen passing up the perpendicular trunks, clinging to 

 the bark with its claws in a manner not dissimilar to that of 

 the squirrels. This method of climbing is doubtless true of all 

 the marmosets, and the lack of opposability of the hallux and 

 pollex is correlated with the possession of sharp compressed 

 claws instead of flattened nails. 



The tri tubercular upper molars furnish another character of 

 considerable importance in determining the relationship of the 

 marmosets to the other groups. No Primate of the Eocene is 

 known to possess fully quadritubercular molars. Some of the 

 Adapidse have a rudimental fourth cusp, but the crown can 

 not be said to be as fully quadritubercular as that of the higher 

 modern apes. By far the greater number of the species have 

 simple tritubercular upper molars, and with the exception of 

 the marmosets and Tarsius all the modern representatives of 

 the Anthropoidea have four fully developed cusps. It follows, 

 therefore, that these two groups are survivals from this early 

 condition of the tritubercular stage of development of the 

 molars, and that their detachment from the main axis could 

 not have taken place later than the Eocene. The loss of the 

 last molar in the marmosets, while unusual for a Primate, has 

 clearly taken place since that time, as in the Eocene all the 

 known species have three fully developed molars. There is 

 still another feature of importance exhibited by certain of the 

 marmosets, which is worthy of notice. Forsyth Major found 

 that, out of nineteen skulls of Ilajpale examined, in six the 

 lachrymal extends beyond the orbit to such an extent as to join 

 the nasal and exclude contact between the maxillary and 

 frontal.* This is also true of two skulls of this genus in the 

 Peabody Museum, and I am satisfied that this more primitive 

 condition of the lachrymal is by no means of infrequent occur- 

 rence among these species of marmosets. These features are 

 associated with a characteristic lack of depth of the lower jaw, 

 a subglobular form of the condyles, and small size of the lower 

 canines, which do not exceed the incisors, all of which consti- 

 tute so many steps in the approximation to certain of the 

 Paleopithecine apes of the Eocene. Upon the whole, I am 

 fully persuaded that the ancestors of the marmosets must be 

 sought for among the members of this latter group, and that 



*Proc. Zool. Soc. London, Feb. 19, 1901, p. 146. 



