MORRISON MAMMALS: PANTOTHERIA 89 



Docodon Ennacodon 



1. Premolars four. i. P2 lacking. 



2. Molars seven or eight. 2. Molars apparently six. 



3. First molar somewhat smaller. 3. First molar somewhat larger rela- 



tively than in Docodon. 



4. External premolar cingula strong. 4. External premolar cingula weaker. 



5. Mandible stouter and longer. 5. Mandible more slender and shorter. 



Great as these differences appear, none is of generic value. ( i ) Study of a rather 

 extensive series of specimens shows that in these forms P2 is erupted later than Pi and 

 P3-4. Whether it is of the second or first dentition is not clear — so far as has been ob- 

 served its late appearance is not connected with the late disappearance of a predecessor. 

 It is a small tooth and may be in process of disappearance. Its apparent absence in 

 Ennacodon could be due entirely to the youth of these two specimens. This is supported 

 by the existence of another, hitherto unmentioned, specimen which has P2 but which 

 cannot otherwise be separated from Ennacodon crassus. (2) The lower molar number 

 may then be due to the same cause, immaturity. Some jaws of this group have six 

 erupted molars, some seven, and some eight, and those with six or seven have other 

 signs of youth. (3) The apparent slight diflference in the relative size of Mi may be 

 illusory and in any event is of not more than specific value. (4) The same is true of the 

 slight apparent difference in the development of the premolar cingula. (5) The differ- 

 ent proportions of the jaw are such as always exist between younger and older indi- 

 viduals of the same species. There are other unimportant differences which serve to 

 separate the two species Ennacodon crassus and Ennacodon affinis but are not common 

 to the two in distinction from Docodon. It is impossible reasonably to maintain that 

 Ennacodon and Docodon are separate genera. The species are retained and are re- 

 ferred to Docodon. They do have some slight differences from the other species now 

 referred to this genus, but these are so unimportant, and even doubtful, that their real 

 validity can only be tested by a still larger series of specimens than is now available. 

 It is probable that Docodon includes more than one species, and perhaps as many as 

 four or five, but one must hesitate to vouch for the necessary validity of all of the pres- 

 ent established species. 



Like those of the other pantotheres, the upper jaws referable to this family have 

 not been found in actual association with the lowers. Nevertheless we are relieved of 

 the necessity for creating a special genus for them by the placing of all the lower jaws 

 in a single genus. There is no question, as pointed out above, that these upper jaws do 

 belong in this family and they clearly can be placed in the one American genus, Doco- 

 don. It is now impossible, however, to separate the upper jaws into species or to place 

 them in one or another of the four species based on lower jaws. They are therefore 

 placed provisionally in a distinct species, Docodon suferus, to serve for purposes of 

 description and reference until association can be demonstrated. 



