MORRISON MAMMALS: PANTOTHERIA 53 



Archaeotrigon sp. indet. 



Material. — Y.P.M. No. 13642. Lower jaw with last M. 



Horizon and Locality. — Morrison formation, Quarry 9, Como Bluff, Wyoming. 



This specimen is of some interest in showing the last molar in Archaeotrigon and 

 much of the posterior part of the mandible. The last molar is much like the preceding 

 teeth in this genus, but smaller, being only i.i mm. in length and hence probably M4. 

 The angular process is quite unlike that in the Dryolestidae and has much resem- 

 blance to Peramus. It is small, triangular, and projected downward and backward. 



r^/A/Wow Simpson 1927 



1927. Tanaodon, Simpson, Amer. Jour. Set. (5) XIII, 410 — non Taiiaodon Kirk 1927. 

 1927. Tathiodon, SimT^son, Amer. Jour. Set. (5) XIV. 



Definition. — Cheek teeth six or seven. Paraconid distinct and stout, but not 

 high. Talonid triangular in plan, with a posterointernal cusp. Metaconid higher, 

 stouter, less sharply pointed than in Archaeotrigon or Paurodon. No postcanine dia- 

 stema, molars not spaced. Horizontal ramus slender. Symphysis long. 



Type. — T. agilis Simpson. 



Distribution. — Morrison formation, Wyoming. 



The name Tanaodon, originally applied to this genus, was given almost simul- 

 taneously but a little earlier to a Chinese Devonian mollusc. The mammal was there- 

 fore renamed Tathiodon two months after its original description. The molar type here 

 displayed is more like that of the dryolestids than is that of any other paurodontid, but 

 Tathiodon is at once distinguished from the Dryolestidae by the low number of cheek 

 teeth and by the still relatively elongate molars, with roots unspecialized. A single 

 species is known. 



Tathiodon agilis {^\xn^%OT\ 1927) 



1927. Tanaodon agilis, Simpson, Amer. Jour. Sci. (s) XIII, 410. 

 1927. Tathiodon agilis, Simpson, Amer. Jour. Sci. (5) XIV. 



Type. — Y.P.M. No. 13649. Left lower jaw with two molars. 

 Horizon and Locality. — Morrison formation, Quarry 9, Como Bluff, Wyoming. 

 Diagnosis. — Sole species of the genus. Lengths of two preserved molars, probably 

 M2-3, 1.35 and 1.5 mm. respectively. 



Dentition 



The interpretation of alveoli is notoriously difficult, but an attempt is necessary in 

 this case. At the anterior end of the jaw are three or four alveoli manifestly for incisors. 

 Then follows an alveolus not larger than the following ones but not quite in line with 

 them and pointing a little forward. This must have lodged the canine. Alveoli for two 

 premolars follow, then there is a break from which the bone is missing, but since the 



