48 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



might add Knightomys senior, shows a development between para- 

 myids and typical sciuravids. The resemblances would seem to be 

 toward, for example, the Cathedral Bluffs Microparamys and decid- 

 edly away from such forms as Mysops. 



DAWSONOMYS WOODI Gazin 



(Plate 5, figure 7) 



Dawsonomys woodi was proposed (Gazin, 1961) as a new genus 

 and species for the La Barge form represented by the lower jaw 

 (U.S.N.M. No. 19309) that was cited in 1952 as "Sciuravus, possibly 

 S. depressus Loomis." The generic characters may again be sum- 

 marized as follows: Cusps of teeth low, but with metaconid of P4 

 high and well forward. Trigonid of Mi broad and anteroposteriorly 

 compressed, but with small, distinct trigonid basin. Talonid basin 

 large and comparatively shallow. Ectolophid low with distinct meso- 

 conid. Entoconid low and lophid from entoconid low but well defined 

 and joins hypoconid. Posterolophid extends nearly to lingual margin 

 and close to but sharply separated from the crest extending buccally 

 from the entoconid. 



The species was observed to be appreciably smaller than Sciuravus 

 nitidus but diagnostic characters at this level were not otherwise distin- 

 guished from those cited as characterizing the genus. 



Direct comparison of the type of Dawsonomys woodi with the 

 lower jaw that Loomis cited as a cotype of "Sciuravus" depressus 

 has indicated that they do not represent the same species and clearly 

 not the same genus. Mi in the Lysite jaw (A.C.M. No. 458, see pi. 5, 

 fig, 9) has a much narrower trigonid, a larger talonid basin, and the 

 mesoconid is more marginal in position. The most noticeable differ- 

 ence, however, is in the lophid from the entoconid which is weaker, 

 much closer to the posterolophid, and appears scarcely more than a 

 slight bifurcation of the posterolophid at the hypoconulid. In the 

 latter respect the Lysite jaw rather resembles Mi in the Cathedral 

 Bluffs Microparamys jaw (P.U. No. 16112), 



Loomis's type of "Sciuravus" depressus is a skull (A.C.M. 

 No. 432) portion with three molars preserved (see pi. 5, fig. 8) and 

 while no direct comparison between D. woodi and the upper teeth of 

 "S." depressus can be made, the pattern of the latter seems surely 

 sciuravid rather than paramyid. The crests of the upper teeth are 

 subdued, but I note that the metaconulid joins the metaconid, possibly 

 somewhat more as in Taxymys than as in Sciuravus. Kelley and 

 Wood (1954) have noted that Loomis's species does not belong to 

 Sciuravus. 



