126 



osborn: OLIGOCENE, MIOCENE, pliocene eqtjid^e. 



Type. — Amer. Mus. Cope Coll. 8347. A complete skull, finely preserved, teeth one-fourth worn, with associated 

 vertebra; and parts of fore limb. This skull was referred by Cope to Hippotherium speciosum Leidy (= Hippodon spccio- 

 sus), an. indeterminate species. Referred specimen, lower jaws, Amer. Mus. Cope Coll. S341, from the same locality and 

 formation. 



Type figure. — Plates 10.1, 17.7, text Fig. 99 of this Memoir. 



Characters. — (Matthew, 1913) (1) Medium size, p'-m 3 .0255; (2) protocone separate about half way down, oval on 

 premolars, somewhat flattened on molars; (3) enamel of fossettes strongly folded to about half way down the crown, 

 (4) double pli caballin fold, as in M. calamarius; (5) plication of enamel of metaloph and hypostyle region more elaborate 

 and branching than in M. calamarius; (6) metastylid of po posterior in position; (7) metaconid pillar distinct but very 

 small; (8) metastylid moderately separated in p2, in iri3 by shallow groove, anteroexternal cingulum fold distinct in half worn 

 teeth. (9) Lachrymal fossa rather small and shallow, not sharply marked; (10) no malar fossa; (11) preorbital region 

 short; (12) postcanine diastema one-fifth length of cheek teeth. Foot characters based on doubtfully referred speci- 

 mens; (13) metacarpals short, moderately slender, lateral digit complete though considerably reduced; (14) trapezium 

 nodule very small and solidly coossified with trapezoid. 



Among the above characters those assigned to the lower jaw are based on specimens of somewhat doubtful reference. 



This species seems to represent an advance upon the M. calamarius type in the more extreme plication of its enamel 

 foldings. 



6 



Fig. 100. Type of Mcrychippus patruus Osborn, Amer. Mus. Cope Coll. 8347a, p 3 -m 2 . Natural size. 



Merychippus patruus sp. now 



Plate 17.6. Text Fig. 100. 



Horizon and locality. — Driftwood Creek, Republican River formation, Nebraska, Peraceras or Upper Procamelus 

 zone, Lower Pliocene. This type was found near the type skull of M. republican us. Type collected by W. Brous, 

 1879. 



Type. — Amer. Mus. Cope Coll. 8347a. Left upper jaw containing p 3 -m 2 . 

 Type figure. — Plate 17.6, text Fig. 100 of this Memoir. 



Characters. — (Matthew, 1913) (1) Of medium size. (2) Premolars relatively narrow transversely, molars rela- 

 tively broad transversely ; (3 ) in well worn teeth protocone strongly united to protoloph ; (4) protoloph separated from 

 metaloph until teeth are considerably worn; (5) hypocone absorbed in metaloph at an early stage of wear, distinct only 

 in nr of the type; (6) protocone of round-oval form, anterior in position; (7) enamel lakes in well worn teeth nearly 

 simple; (8) pli caballin fold of crochet region single in well worn teeth, crochet triple in unworn teeth; (9) parastyle moder- 

 ately broad on upper premolars, narrow on upper molars; (10) metastyle narrow in all teeth, narrowing rapidly at the 

 base. 



The name M. patruus (Latin, patruus meaning father's brother) is suggested by Matthew in reference to the supposed 

 affinity of this animal to Protohippus parvulus, the Pliocene stage, from which M. patruus is distinguished by (1) larger 

 size, (2) by the shorter crowns of the teeth, (3) the sudden narrowing of the mesostyle, as well as (4) by the transverse 

 narrowness of the premolars. 



