THE AFTONIAN HORSES 347 



transverse diameter as the crown wears away/ 5 In the present case the 

 teeth are the only parts available for study, but these are in such perfect 

 accord with the teeth of Equus scotti Gidley that there need be little hesi- 

 tation in referring them to that species. Equus scotti has been recog- 

 nized with doubt in collections from the Sheridan beds near Hay Springs, 

 Nebraska, 8 a point farther north than southwestern Iowa and equally as 

 far from the type locality. 



The collection contains a few teeth of smaller size, agreeing in dimen- 

 sions and in the enamel foldings with teeth which have been referred to 

 Equus complicatus Leidy. A superior third molar, number 128, from 

 Missouri Valley, shows a very complicated pattern, even though consider- 

 ably worn. Its dimensions are: transverse diameter, 24 millimeters; 

 antero-posterior diameter, 27 millimeters; length, 60 millimeters. An 

 Aftonian gravel pit at Turin, Iowa, has furnished an imperfect superior 

 molar, number 122, intermediate between the first and the last of the 

 series, but its exact position undetermined, which shows a transverse 

 diameter of 28 millimeters and a length of 70 millimeters. The anterior 

 fourth of the tooth has been split off, but what remains shows very com- 

 plicated enamel foldings. Another tooth, number 124 (plate 21, figure 

 3), of somewhat simpler pattern, but still sufficiently intricate to belong 

 to E. complicatus, is from the Cox pit at Missouri Valley; it is 28 milli- 

 meters in transverse diameter, 29 millimeters antero-posteriorly, and 70 

 millimeters in length. Tooth number 121 (plate 21, figure 4) is also 

 from the Cox pit; it is 75 millimeters in length, but little worn; the 

 enamel pattern is much simpler than in any of the other teeth so far 

 noted. It agrees with Equus excelsus and E. occidentals in the absence 

 "of the little enamel fold near the bottom of the deep valley between the 

 protocone an'd the hypocone." It is 28.5 millimeters in transverse diam- 

 eter and 30 millimeters from front to back. In size and pattern, how- 

 ever, this tooth is almost identical with Gidley's figure 3 A, in the Ameri- 

 can Museum Bulletin, volume xiv, page 97, and this figure is described 

 as a molar of Equus complicatus. If the teeth illustrated in figure 3, 

 page 97, and in figure 7, page 109, of the bulletin above quoted may be 

 referred to one species, then all the superior molars from the Aftonian 

 gravels of southwestern Iowa may be arranged under two species distin- 

 guished by differences in the size of the teeth, namely, Equus scotti Gid- 

 ley and Equus complicatus Leidy. 



A specimen which can not with certainty be referred to the Aftonian 

 gravels may be worthy of note. A few years ago there was received from 



8 W. D. Matthew : List of the Pleistocene fauna from Hay Springs, Nebraska. Bulletin 

 of the American Museum of Natural History, vol. xvi, 1902, p. 317. 



