NO. 1689. THE FO^^IL CENUS PTff.OnUS—GIDLEY. 613 



Chiro,r, now known to be Ptilodvs also, has been shown by Osborn to 

 hold a similar relationship to Bolodon, a contemporary of Flaglav- 

 Jax, and similarly known only from the upper teeth. There seems, 

 therefore, little doubt that, as in the case of Ptilodus and Chirox^ 

 the genera Flagicmlax and Bolodon were founded on the lower and 

 upper teeth, respectively, of individuals represent in<>j the same species 

 or, at least, species not generically distinct. If this be true, the 

 family Bolodontida? is also invalid. 



With the important addition to our knowledge of the Allotheria 

 supplied by this more complete material from Montana, the neces- 

 sity of a further revision and reclassification of the whole group 

 becomes apparent. The present paper is intended, however, only as 

 a preliminary communication, hence it is confined principally to the 

 Ptilodus group. 



Family PLAGIAULACIDiE Gill. 

 Genus PTILODUS Cope. 



Generic characters. — With the added characters shown in the new 

 specimen described below, the genus Ptilodus may now be redefined 

 as follows: 



Dental formula.— i\, c^, pm|, m|. Incisors simple with sharp, 

 pointed tips, upper and lower pairs not directly opposing each other; 

 ui)per canine and first three premolars well developed and functional, 

 though not directly oi)posing the teeth of the lower jaw ; p" with 4 to 

 G cusps; p* the largest tooth of the upper series, greatly elongated 

 anteroposteriorly, multituberculate ; m^ multituberculate, with two 

 complete rows of tubercles and a third vestigial row, confined to the 

 posterior half, on the inner side of the crown; m- shorter and broader 

 than m\ with three short rows of tubercles. In the lower jaw, p^ 

 and p. are wanting and p. is rudimentary, with a rounded bead-like 

 crown, Avhich fits into a depression at the anterior end of the large 

 p, ; p^, the principal tooth of the lower series, greatly elongated and 

 laterally compressed, forming a thin cutting blade with numerous (12 

 to 14-) parallel ribs on either side. 



PTILODUS MEDI^VUS Cope. 



Ptilodus mcdicevns Cope, Amer. Naturalist, XV, 1881, p. 921. 



Types pechnen. — A single lower fourth premolar. (No. 8019, 

 Amer. Mus. Nat. Hist. Coll.) 



Neotype (Cope).— Portion of a right lower jaw representing the 

 complete lower dentition. Amer. Mus. Nat. Hist. Coll.'* 



Type-locality. — Northern New Mexico. 



Horizon. — Torre j on formation. 



"Cope, Amer. Naturalist, 1884, p. 694; Rep. U. S. Geol. Surv. Terr., Ill, p. 1, 

 1884, pi. xxiiid, fi^. 1. 



Proc.N.M.vol.xxxvi— 09 43 



