320 SYNOPSIS OV THE VERTEHRATE FAUNA OF THE PtJERCO SERIES. 



referred to Sarcothraustes it is well developed, although small and conic in shape, 

 and occupies an elevated position on the inner side of the front of the crovi^n, close to 

 the fourth cusp. In the M. interrnptus, it is less distinctly developed, and is wanting- 

 from the last molar in some of the specimens. In M. acolytus the fifth cusp adheres 

 closely to the fourth, and is in some specimens wanting. In the M. suUrigonus the 

 fifth cusp is indifferently absent, or present in small development on the second and 

 third molars. In nearly all the species of the genus as here constituted the fifth cusp 

 is present on the first inferior true molar ; but in the M. turgidus and species most 

 nearly related, it is absent. The species of the latter type differ from the forms allied 

 to M. coryplums and M. ferox in their robust premolars, but the M. opistliacus fur- 

 nishes a passage between the two. It does not seem practicable to divide the genus, 

 as I once proposed,* on the presence or absence of an interior cusp of the third supe- 

 rior premolar. While this cusp is present in the M. turgidus, it is wantingf in the 

 nearly allied M. zittelianus, and the M. opistliacus. 



In the species referred to the second section of the genus (Goniaeodon, type M. 

 levisanus), the fifth cusp is quite distinct, but is median in position and near the base 

 of the crown (except in M. Iieilprinianus), forming an anterior angle in the outline of 

 the crown. These species I have referred sometimes to TriTsodon and sometimes to 

 Diacodon, but I think I have now found their proper position. 



With six new species now added, the total of those embraced in the genus is 

 twenty-four. 



Parts of the skeleton of M. antiquus, M. coryphcms, M. levisanus, M. foverianus, 

 M. corrugatus and M. ferox are preserved, and do not present any but specific differ- 

 ences. I must here correct an error into Avhich I fell in describing the M. ferox (Ter- 

 tiary Vertebrata, p. 331) in calling the fibula the radius (Plate XXIV f, fig. 11). The 

 distal part of this element is very robust in that species. 



I. Inferior true molars with anterior triangle of three cusps [Sareothraustes). 

 Length of inferior premolars, .009 ; depth of ramus at p. m. iv, .055 ; superior true molar ii, .023 by .016, M. antiquus. 

 Inferior true molars, .052 ; premolars, .043 ; infer, m. iii, .015 ; depth of ramus at m. i, .052; length sup. true molars, 



,040 M. conidens. 



Inferior true molars, .037 ; premolars, .047 ; depth ramus at p. m. iv, .041 M. bathygnathua. 



Last inferior true molar, .012 ; depth of ramus at m. ii, .036 M. crassiewpis. 



Inferior molars, .037 ; :n. iii, .012 ; premolars, .037 ; sup. molars, .030 ; depth ramus at m. iii, .037 M. eoryplmus. 



Inferior molars, .030, wide; premolars, .030, close together, the first subconic ; ramus at ni. i, .020 3J. peiitiicus. 



Superior molars, .030 ; depth ramus at inferior m. ii, .035 .V. gaudriaims. 



Inferior true molars, .019; premolars, .018, the anterior spaced, the first anteroposteriorly short ; depth ramus at m. 1, 



.013 M. ikterruptus. 



Inferior true molars, .018 with anterior elevated ledge and basin-like heel ; depth at m. i, .014 31. lydekkerianm. 



* Proc. Amer. Phil. Soc, 1883, p. 312. f Genus Oxyctenus Cope, 1. c. 



