290 THE WASATCH AND BKIDGER FAUNiE. 



of the superior series. The depth of tlie mandibular ramus is taken at the 

 penultimate true molar. 



I. Length of true molars les.s tliau .0140. 



Length of true molar.s, .0135 ; premolars less extended 8. viverrinus. 



Length of true molar.s, .0112 ; premolars much larger S. minor. 



II. Length of true molars from .0180 to .0220. 



True molars, .0183; depth of ramus, .0080; first true molar small. . . S.cayluai. 



Tiue molars, .0200; depth of ramus, .0100; heels of molars large, 



wide 8. pungens. 



True molars, .0220 ; depth of ramus, .0125 8. secundarius. 



True molars, .0210; depth of ramus, .0150; heels large; first molar 



not reduced 8. multictispis. 



True molars, .0220; depth of ramus, .0150; heels very narrow and 



short ... 8. brevicaJcaratm. 



True molars, .0220 ; depth of ramus, .0180 ; heels elongate, basin- 

 shaped 8. whitice. 



III. Length of true molars exceeding .0230. 



Length of true molars, .0235 ; depth of ramus, .0210, robust 8. strenuus. 



Length of true molars, .0250; premolars large; ramus slender; 



depth, .0140 8. aculeatus. 



There is some diversity in the form of the astragalus in the species 

 above named. There may be two generic forms included here, the one 

 having the astragalus without trochlear groove, represented by S viverri- 

 nus., the other with the tibial articular face of that bone slightly concave, 

 represented by the S. whitice. As the latter sti*ucture is the later in its 

 appearance in time, it is presumably that of Stypolophus pungens, the tj^pe 

 of the genus which is from the Bridger formation. For the older form, 

 the name Protototnus (Cope, 1874) must be used. P viverrinus and P. 

 Mans are certainly referable to it. 



Stypolophus insectivoeus Cope. 



Proceed. Amer. Philos. Soc, 1)J72, p. 4C9; Paloontological Bulletin No. :',, i>. 1, publUlied August?, 1872. 



Plato xxiv, figs. 10-11. 



Represented by a posterior molar and a premolar of the right side of 

 an animal less than half the size of the S. pungens Cope. The molar pre- 

 sents three anterior trihedral acute tubei'des, of whit-h the exterior is more 

 elevated than tlie others. Its posterior plane forms one transverse face with 



