348 S. CALVIN AFTONIAN MAMMALIAN FAUNA 



Mr John H. Charles, of Sioux City, the fragment of a maxillary with 

 five molar-premolar teeth in place, shown in plate 20. The third molar is 

 missing. The sender was not certain of the exact locality or the geological 

 horizon from which the specimen came, but he added the information that 

 similar teeth had been found in a sand pit along the Big Sioux river. 

 The teeth referred to in this last statement are those mentioned by Bain 

 in his report on the geology of Woodbury county, 9 and pronounced by 

 Cope to be "three left superior molars of the horse, Equus major Dek., of 

 Pleistocene age." The sand pit which furnished the teeth submitted to 

 Cope is now known to be a part of the same series of Aftonian deposits 

 recently described from Monona and Harrison counties. The teeth illus- 

 trated in plate 20 are, beyond much question, from the Aftonian horizon, 

 though satisfactory proof is lacking; they are more completely worn out 

 than any of the other teeth in the collections, having been cut away by 

 use almost to the fangs. The first molar has actually been ground 

 through to the lower end of the enamel which surrounded the anterior 

 lake. The transverse diameters are : p 2 , 24.5 millimeters ; p 3 , 27 millime- 

 ters ; p 4 , 28 millimeters ; m 1 , 26 millimeters ; m 2 , 26 millimeters. Length 

 of the series from the sharp anterior enamel fold of p 2 to the posterior 

 edge of the metastyle of m 2 , 137 millimeters; the corresponding dimen- 

 sion in the Gladwin horse, referred to Equus scotti Gidley, 155 milli- 

 meters. The teeth of the Sioux City horse represent a stage of wear even 

 more advanced than Gidley's A 3 , figure 3, page 97, of the bulletin above 

 quoted. Without hesitation they may be referred to the species Equus 

 complicatus Leidy, the great simplicity of the enamel pattern being ac- 

 counted for on the basis of changes due to wear. 



Of the lower molar-premolars there are two well marked types which 

 probably correspond to the two species, Equus scotti and Equus compli- 

 catus. The left mandibular series of the Gladwin horse, shown in plate 

 17, figure 2, illustrates one of these types. The teeth have very thick 

 cementum and are unusually heavy; the transverse diameters measured 

 in millimeters, exclusive of the cementum, are : p 2 , 18 ; p 3 , 19 ; p 4 , 21 ; m 1? 

 17. The other molars are broken and can not be measured. The thick- 

 ness of p 4 , including cementum, is 24 millimeters. The length of the 

 series antero-posteriorly is 195 millimeters. Another notable feature of 

 these teeth is the great thickness of the enamel. The same thick enamel 

 and massive character are seen in the two inferior molars of figure 6, 

 plate 19, the specimen illustrated being from the Cox pit at Missouri 

 Valley. This specimen may without doubt be referred to the same spe- 



9 H. Foster Bain : Geology of Woodbury county. Iowa Geological Survey, vol. v, 189G, 

 p. 277. Following Todd, Bain believed tbis sand was preglacial. 



