FORT UNION OF CRAZY MOUNTAIN FIELD, MONT, 115 



almost certainly referable to this genus but is shown to be a dis- 

 tinctive species even from the one very fragmentary specimen avail- 

 able. Ml is 1.2 and M3 1.1 mm in length. The comparison with 

 L. ladae by d/«T is thus as follows: 



LMi:4.7 LMa-.e.S 



The ratio LM1/LM3 compares as follows: 



L. tener (referred specimen) ".0.86. 



L. ladae (three specimens) : 1.00-1.07, mean 1.05. 



L. munusculuni: 1.09. 



M3 is thus more reduced in L. ladae and in L. munusculum than 

 in L. tener. The difference between L. munusculum and L. ladae may 

 be, but is not shown to be, significant. 



Genus MYRMECOBOIDES Gidley 



Myrmecoboides Gidley, 1915, p. 395. 



Type. — Myrmecoboides monianensis Gidley. 



Distribution. — Middle Paleocene, Fort Union, Montana. 



Diagnosis. — Canine of moderate size. Premolars well spaced. 

 P4 elongate, with strong but low, median paraconid, metaconid well 

 separated and nearly as high as protoconid, talonid long and narrow 

 with small, subequal hypoconid and entoconid and hypoconulid 

 barely suggested. Molars, particularly M3, -with, long talonids and 

 with moderately elevated trigonids. Paraconids smaller than meta- 

 conids but nearly as high and partly connate, so that paraconid and 

 metaconid together form a twinned apex that is higher than the 

 protoconid. 



Remarks. — Gidley stated that the name Myrmecoboides was "given 

 to the ancient form on account of its likeness to Myrmecobius rather 

 than as a positive assumption of real relationship." He did, however, 

 state that the genus was marsupialian and probably related to the 

 Myrmecobiidae, and he went into much detail regarding its bearing 

 on marsupial evolution. Abel (1919) placed Myrmecoboides in the 

 Myrmecobiidae. Osgood (1921) stated that Myrmecoboides might 

 well be ancestral to Caenolestes, if it was a marsupial. Sclilosser (1923) 

 classified it in the Myrmecobiidae but noted that it might not be mar- 

 supial. Longman (1924) gave a resume of Gidley's view, stating (as 

 had Gidley) that the resemblances to Myrmecobius were suggestive 

 but not conclusive. Matthev/ (1916) had, however, quickly pointed 

 out that the characters of Myrmecoboides are not myrmecoboid or 

 marsupial, but leptictid and placental. Gidley also came to accept 

 this conclusion (personal communication) but apparently did not 

 publish this fact. Students of Paleocene mammals have long realized 

 that Myrmecoboides cannot be a marsupial, but aside from Matthew's 

 brief statement, which has been overlooked by almost all later com- 



