336 E. L. Troxell — Early Pliocene One-Toed Horse. 



Professor Lull have generously helped me in many ways, espe- 

 cially in the beginning of the work. Professors Schuchert and 

 Oshorn very kindly allowed me to study the material in their 

 respective museums. 



II Pliohippus lullianus sp. nov. 



The specimen here described was the skeleton of a young 

 colt about ten mouths old. The milk teeth are all visible and 

 some are slightly worn ; the first permanent true molar is well 

 formed and about ready to be cut — it has, however, no apparent 

 cement. The loose epiphyses and the incompletely ossified 

 bones also attest the immaturity of the individual. 



Vestigial teeth. — The canine teeth of both the upper and 

 lower series are scarcely so large as the lead of a pencil, diam- 

 eter I - 3 n,m , but are about 7 n,m in length. In life it is quite 

 probable that they did not appear above the gum, but lay 

 along the alveolar border and, of course, were not functional. 

 The first deciduous molar, commonly called the wolf tooth, in 

 the upper jaw is large, 17 mm antero-posteriorly, and in a later 

 stage of wear might have been functional. The corresponding 

 tooth in the lower jaw, like the canines, is vestigial ; it meas- 

 ures l-5 mm in diameter and standing erect in front of the larger 

 tooth, protrudes 2 mm from the bone. The length, root and all, 

 is about 7 mm . This tooth is not quite so large as one from a 

 small skull of Mesohijopus ; the latter has a distinct crown, 

 while in the former the diameter is uniform throughout. 



Permanent molars. — Two uncut, permanent molars were 

 secured, one upper and one lower. Although the upper molar 

 is broken, it shows well certain characters which will be diag- 

 nostic of the species. The crown in its present development 

 is less than 40 mm long; it is slightly curved antero-posteriorly, 

 but the pronounced transverse curve of the horses' teeth of 

 that period is not conspicuous ; however, since the tooth is not 

 fully formed this observation may be of less importance. 



The diameter of the tooth at the crown, measured over the 

 styles, is 30 mm ; l cra lower it is 27 mm and here the width across 

 mesostyle and protocone is 25 mm . With still further wear the 

 longitudinal diameter would become less than the transverse. 

 The lakes are broad and very simple in pattern ; the horns are 

 quite long and smoothly curved, while the enamel in places is 

 very thick. The protocone, which does not extend anterior to 

 its junction with the protoconnle, is very long (10 mm ), but 

 rather narrow transversely (5 rnm ). The sides are parallel for 

 quite a distance, making it unlike the round or oval cone of 

 Protohippus. There is a sharp, thin fold, the plicaballum, 

 between the protocone and the metaconule, which is commonly 



