18 Annals of the Carnegie Museum. 



Ramus of mandible moderately long and slender ; masseteric fossa large 

 and deep ; teeth rather heavy and zvith low cusps ; lower premolars 2, 

 J, and 4 two-rooted, cusps simple, oblojig, lens-shaped i?i horizontal sec- 

 tion, with one outer convex and two inner concave surfaces ; molars 

 with anterior trigon and a lower tuberculate heel, external cusps higher 

 than iftternal cusps. 



Nearly all of the teeth are somewhat worn. P and P^^ are longer 

 than P^-. The outer faces of the premolars are very convex and are 

 quite low-crowned. My has a heavy antero-external and a small an- 

 tero-internal cusp. The anterior accessory cusp is minute. The heel 

 is low but the external portion is highest. As seen from the outside, 

 the latter is tuberculate. M has nearly the same form and size as 

 My but Mg^ is smaller. I do not know of any species with which this 

 can be closely compared. From Silberling quarry east of Bear Butte, 

 Montana. 



mm. 



Length of portion of mandible preserved 34. 



Depth of mandible under Mij 5-^ 



Length of last three premolars 8. 



Length of molar series 8.7 



Megopterna minuta gen. et sp. nov. 

 (Plate I, figures 5-6.) 



(Type No. 1675, Carnegie Museum Catalogue of Vertebrate Fossils.) 



The type consists of a portion of a mandiblewith two teeth attached, 

 probably a last lower premolar and a first lower molar. From the 

 same locality as the types of Picrodus silberlingi, and Coriphagus 

 montanus. 



Size mifiute, mandible deep in proportion to the height of the teeth ; 

 P-^ not showing distinct cusps, but with a raised inner border, the longest 

 diameter being antero-intei'tial and posiero-external ; J/y with three dis- 

 tinct anterior cusps, and a posterier basin-shaped heel much larger than 

 the anterior trigo?i, tvhich is bounded externally by two distinct tubercles 

 and posteriorly and internally by a raised border. 



The mandible is nearly as deep under My as the combined lengths 

 of Py and My. The first premolar is so minute and the surfaces of the 

 enamel reflect so much light, that it is difficult to figure its exact shape, 

 yet the figure gives a very good idea of the form of the tooth. The 

 outer surface of the tooth had perpendicular ridges and depressions. 

 The top is nearly flat, but bounded postero-internally by a raised 

 border. 



