‘ 
328 Bulletin American Museum of Natural History. [Vol. XXXIV. 
. Bighorn Valley include remains of a number of genera and species of ‘Tri- 
gonolestidee, comparison of which with the lower molar of Diacodexis enabled 
Mr. Granger to recognize its real relationship. 
The upper molars are unquestionably Hyopsodus and agree with speci-_ 
mens referred to H. powellianus Cope 1885. (P. zuniensis Cope,’ 1882, 
Les) 
Of the three specimens, No. 4202, a., b. and ec. which constitute co-types 
of Diacodexis laticuneus, the jaw fragment with m3 must apparently be taken 
as lectotype. It is the first described specimen, as its characters form the 
basis of the specific distinctions given in the key to the species of Phenacodus 
on p. 12 anda reference to this characterization precedes the description of 
‘the upper molars in the species description on p. 19. It is the specimen 
upon which the species name is obviously based. And it is a correspond- 
ing part to the type specimen of P. primevus which Cope had described 
in 1873, on the evidence of a last lower molar. The m3 of “ Phenacodus”’ 
laticuneus agrees sufficiently with the type m3 of P. primevus to suggest 
its belonging to the same genus; this suggestion was evidently confirmed 
in Professor Cope’s mind by comparison of the upper molars, No. 4202b, 
with those of other species of Phenacodus, P. primevus and P. (now Tetra- 
clenodon) puercensis. 
The lower jaw fragment therefore was the primary basis of the specific 
distinctions and in part the basis of the generic reference of the original 
description of P. laticuneus, and is the first of the cotype specimens to be 
described. Following the intent of the author so far as ascertainable? 
it should therefore be selected as the lectotype- 
Diacodexis thus stands as a genus of Eocene Artiodactyla, not as a 
synonym of Hyopsodus, and the name has been so used by Dr. Sinclair, 
preoccupying 7rigonolestes of later date. 
1 This is not P. zuniensis Cope 1881 (Proc. Am. Phil. Soc., XIX, 492), which was referred 
by Matthew in 1897 to Tricentes subtrigonus. 
2 See Catalogue of Type Specimens U. S. National Museum, Introduction, p. 12. 
’ Sinclair 1914, Bull. A. M. N. H., Vol. XX XIII, p. 289. 
