1892.] NATURAL SCIENCES OF PHILADELPHIA. 301 



trenchant protoconid and a talon of two trenchant cusp?, of which 

 the external is much the higher and more acute. Seen from the 

 outer side, this tooth closely resembles the corresponding one of 

 Dissacus, differing only in the presence of the tetartoconid. In the 

 molars the trigonid rises considerably above the talon and is com- 

 posed of a high, sharp and massive protoconid, of a small, low 

 metaconid, and a still smaller and lower paraconid ; the two latter 

 cusps are on the same antero-posterior line and, in m^ at least, are 

 not visible from the external side. The talon consists of a high and 

 sharp hypoconid with trenchant anterior edge and internally three 

 very much smaller cusps, representing the hypocouulid, entoconid 

 and a tubercle in front of the latter to which no name has been 

 given. This crenulate inner border of the talon is highly charac- 

 teristic of the genus. 



Three species : T. quivirensis Cope, T. bleulminatus Cope and 

 T. (MiocJcenus) heUprinlanus Cope. In his last publication'^ Cope 

 refers the T. heilprinianus to a subgenus (Goniacodon) of Mio- 

 dcetius, but the talon of the only known tooth agrees best with that 

 of Triisodon. 



GONIACODON- Cope. 

 Syn Mioclcenus Cope, in part ; Triisodon Cope, in part. 



Though established only as a subgenus of Mioclcenus, this group 

 of species should be raised to full generic rank ; it is closely allied 

 on the one hand to Triisodon and on the other to Sarcothraustes, 

 the distinction between the three being frequently a matter of much 

 difficulty. The species are of moderate size, smaller on the average 

 than those of either of the allied genera. The anterior upper pre- 

 molars are small and simple. ^ is implanted by three fangs (at 

 least in G. levlsanus) but has no distinct deuterocone. P^ has a 

 very high, acute protocone and well developed deuterocone. The 

 upper molars are triangular in shape with low, conical cusps and 

 m^ has a fairly well developed hypocone. P* has a small talon, 

 divided into minute outer and inner cusps. The lower molars are 

 the characteristic feature of the genus ; the trigonid is moderately 

 elevated above the talon ; the proto- and metaconids are of nearly 

 the same size and very closely approximated, forming a twin cusp 



1 Amer. Naturalist, 1881, p. 667. 



2 Trans. Am. Pliil. Soc, Vol. xvi, Pt. II, p. 321. 

 ^ Loc. cit. 



