36 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



is seen in the relatively smaller fourth premolar than in Tetonius 

 homunculus. 



Description. — The formula for the lower dentition of Tetonoides 

 pearcei is 2, T, J, r- The anterior incisor is enlarged but moderately 

 erect, as in T. homunculus, and the second of the two incisors is 

 small with its elongate root posterolateral to the other. The canine 

 alveolus is of moderate size with a more nearly circular outline than 

 the others. An alveolus for a P2 is only a little smaller than that of 

 the canine in the type and in Y.P.M. No. 14084, but anteroposteriorly 

 more flattened in U.S.N.M. No. 22383. The presence of P2 in T. 

 pearcei is a rather primitive feature in comparison with Tetonius ho- 

 munculus, as it is for anaptomorphids in general, and may well be sus- 

 pected for T. tenuiculus also, although none of the known lower jaws 

 of the latter is sufficiently complete to determine this feature. Larger 

 T. homunculus with its relatively larger P4 shows no evidence of a 

 Pa. P3 in T. pearcei is two-rooted and only a little smaller than P4. 

 It lacks the metaconid seen on P4, and the small paraconid is not de- 

 flected inward as in P4. P4 has the relatively very small size charac- 

 terizing T. tenuiculus, but the outer wall at the cingulum is a little 

 longer anteroposteriorly. The paraconid appears a little higher on P4 

 and the metaconid lower and perhaps less developed than in T. tenuicu- 

 lus, as represented by A.M. No. 15066. The talonid of P4 is much 

 alike in the two species. It is of further interest to note that the ex- 

 ternal cingulum of P4, and of the lower molars as well, is better de- 

 veloped in both T. pearcei and T. tenuiculus than in T. homunculus. 

 Usually P4 and Mi in T. homunculus, with their vertically more 

 elongate outer wall, show little or no evidence of the external shelf like 

 cingulum conspicuous in the smaller form. 



Although the lower jaws of Tetonoides pearcei and T. tenuiculus 

 are alike in certain details, including size, in which they differ from 

 T. homunculus, the molar trigonids (Mg and M3) appear to be sig- 

 nificantly different between the two smaller species. While the inner 

 and outer walls of the crowns converge upward, almost as noticeably 

 as in T. homunculus, so that the apex of the trigonid is relatively nar- 

 row — in comparison, for example, with Anemorhysis suhlettensis — 

 the paraconid in T. pearcei is rather closer to the metaconid than it 

 is in T. tenuiculus. In this respect the crown resembles Anemorhysis. 

 Also it was noted that the crest from the protoconid in the posterior 

 lower molars makes a more pronounced anteroexternal deflection as 

 it extends from the protoconid to the anterior margin of the paraconid. 

 This condition, together with the shorter distance between the apices 



