246 Bulletin American Museum of Natural History. [Vol. XIII, 



(Lydekker, '86) from the Lower or Middle Miocene Bugti Beds 

 of Sind. It is incertce sedis here. 



4. Middle Miocene Stage. 



Sans an ^ Sim or re. 



A. tetradactylum Lartet. — This is the noble species of Sansan 

 (Nos. 3378 male, 2379 female, 2389 female, etc.) and Simorre, 

 represented finely in the Paris Museum. It shows striking re- 

 semblances to A. lemanense, together with all the progressive char- 

 acters which we should expect to find in a descendant, and 

 unquestionably belongs to the same line. The scapula is high and 

 narrow as in dolichopodal types generally. The hind limb 



A m3 '"' "" ''" '^ f"^ '" 



Fig. 9. Aceratkerium {ina'sh'um) tetraiiactylmii. Georgensgemiind. Munich. 



(femur and tibia) is of approximately the same length as in A. 

 lemanense., but the metapodials are longer, and more stilted (Mtc. 

 111=160-180, Mts. 111=135-165), indicating that the phylum 

 was developing a progressive running power. The progressive 

 and retrogressive changes in the skull and jaws are most interest- 

 ing and significant as seen in a magnificent male specimen (No. 

 3378, Loc. Sansan). As compared with A. lemanense note the 

 following 



Skeletal Distinctions. 



Skull. — A slight loss of size, symphysis to condyles of skull = 559, ^. tetra- 

 dactylum ; symphysis to condyles of skull = 630, A. lemanense. Nasals, males 

 (No. 3378) slightly less elongated, similarly notched at sides, roughened or ru- 

 gose distally, but not thickened (a sexual character) ; females (Nos. 2379, 2389, 

 Coll. Lartet) very narrow and elongate, separate in median line, not expanding 

 distally. Premaxillse slender. Occiput elevated, spreading superiorly. Sagit- 

 tal crest lower but still well marked. Premaxillse slender. Jaw with elon- 

 gate symphysis, wide diastema, angle deep, projecting backwards. Manus 

 tetradactyl (Coll. Lartet, Nos. 2518, 2537), with reduced metacarpal V ; lunar 

 of tridactyl type (foreshadowing the loss of metacarpal V, which is now reduced 



