Marsh Collection^ Pedbody Museum. 347 



union of the two rami^of the lower jaw, as in the Rodentia. 

 It is probable that this condition is in some way correlated 

 with the enlargement of the incisors and their final growth 

 from persistent pulps, as seen in the most advanced species. 

 Of the extinct American forms, I recognize two grou]3s, which, 

 on account of the wide differences between them in point of 

 structure, I classify in two distinct families. The structure of 

 one of these groups is imperfectly known, and it is impossible 

 to state with certainty whether or not they are Primates. 

 Osborn has recently proposed"^ to arrange them as a primitive 

 suborder of the Eodentia, Proglires, but there are so many 

 serious objections to such a view that I choose to regard them 

 as Primates allied to Cheiromys. My reasons for such a 

 course will be given after the species have been described. 



The suborder as thus constituted includes three families, 

 defined as follows : 



Incisors reduced to a single pair above and below, enlarged, 

 faced with enamel, and growing from persistent pulps, rodent- 

 like ; premolars reduced to one above and absent below ; molars 

 quadritubercular above and below, and rodent-like in pattern, 

 with tendency to degeneration. Cheiromyidse. 



One pair of incisors above and below, ewlarged, recurved, trans- 

 versely compressed, and slightly twisted ; crowns sheathed with 

 enamel, not growing from persistent pulps, and altogether unlike 

 those of rodents ; cheek teeth in lower jaw reduced to two small 

 stylif orm rudiments inserted immediately behind the large incisors ; 

 upper cheek teeth unknown. Metacheiromyidse. 



One to three pairs of incisors in the lower jaw, with central 

 pair enlarged, having distinct roots, and with crowns sheathed in 

 enamel ; premolars never less than two in lower jaw ; molars 

 tritubercular above, with fourth cusp rudimentary; anterior cusp 

 of trigon present in lower molars ; fourth premolar becoming 

 molariform above and below. Microsyopsidse. 



Family MetacheiromyiclcB fam. no v. 

 Metacheiromys Marshi gen. et sp. nov. 

 The remains upon which this family and genus are founded 

 consist of a single specimen of a fragmentary skeleton, which 

 includes the two upper incisors, with a portion of the pre- 

 maxillary attached ; portions of the back and base of the skull, 

 including an otic bulla; one mandibular ramus, with the 

 entire tooth-border preserved ; the bodies of nearly all the 

 cervicals ; a few dorsals and caudals ; some ribs ; the glenoid 

 cavity of the scapula ; the proximal and distal ends of a hume- 

 rus ; the proximal and distal ends of an ulna; the distal end 

 of a radius ; a portion of the pelvis, and the proximal and 

 distal ends of a tibia. 



* American Eocene Primates, etc., Bull. Amer. Mus. Nat. Hist., June 28, 

 1902. 



