. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 18 bulletin: museum of comparative zoology In the lower jaw the posterior lobe of the third molar is very little relatively than in the next species of Parahippus found in this deposit. Four of the lower dentitions have cement on the molars. Protocone. In most specimens there is only a constriction between the protocone and the protoconule, but in Nos. 3820, 3831, and 3815 the tip of the protocone is separate in a few of the teeth, usually the premolars. This is also the case in some of the isolated teeth. Hesse (manu
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 18 bulletin: museum of comparative zoology In the lower jaw the posterior lobe of the third molar is very little relatively than in the next species of Parahippus found in this deposit. Four of the lower dentitions have cement on the molars. Protocone. In most specimens there is only a constriction between the protocone and the protoconule, but in Nos. 3820, 3831, and 3815 the tip of the protocone is separate in a few of the teeth, usually the premolars. This is also the case in some of the isolated teeth. Hesse (manuscript) reports that he finds the same condition in the specimens from Garvin Gully. Milk Teeth. One specimen ( 3840, Plate 10, figs. 2 and 3) still has the milk teeth. The protocone is large and deeply constricted from the protoconule. The metaloph is connected to the ectoloph but shows no plications. The hypoloph is well developed and projects into the postfossette. The hypostyle and posterior cingulum are well developed. Plihypostyle. Ever since the name plihypostyle was first applied to a feature in the postfossette of horse teeth, there has been considerable confusion regarding the homologies of structures bearing that name. It appears to have been used, at one time or another, for any structure in this area which could not be identified as the hypostyle. Obviously the plihypostyle of Parahippus cf. ncbrascensis (Stirton, Journ. Mamm., 22, p. 434, fig. 3, 1941) is not the homologue of the element bearing Protoconule Protocone. MQZ3922 Hupo/oph Hypodtu/e Hi T ocone Fig. 3. Third upper premolar of Parahippus blackbergi (Hay) showing hypoloph. x 2. that name in Neohipparion cf. eurystyle (ibid, p. 435, fig. 7). By extreme good fortune the fossil Equidae from the Thomas Farm demonstrate the development of the principal features in this area. Some of the specimens of P. blackbergi (Nos. 3820, 3815, and 3829), and a number of isolated teeth, show, on unworn or little worn
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