1270 



CLASS MAMMALIA. 



genus Bolodon, of the Dorsetshire Purbeck. In this genus (fig. 

 1 137) there were apparently three upper premolars and four true 

 molars ; with probably three incisors, of which the first is very 

 minute. Although of much smaller size, the cranium of the type 

 species presents a striking resemblance to that of the African Trityl- 



Fig. 1137. — The right maxilla of Bolodon crassidens ; from the Dorsetshire Purbeck. mx, 

 Maxilla ; fimx, Premaxilla ; _/?, Foramen ; m, True molars ; pm, Premolars ; i, Incisors. Greatly 

 enlarged. (After Osborn.) 



odon. Allodon, from the Upper Jurassic of North America, is a 

 very closely allied, if not identical form, in which there were cer- 

 tainly three upper incisors, of which the second (fig. 1137) is en- 

 larged, and apparently corresponds to the large inner incisor of 

 Tritylodon. The genus Microtestes, from the Upper Trias of Wiir- 

 temberg and England, is only known by de- 

 tached molars (fig. n 38) closely resembling 

 the true molars of Plagiaulax. This genus 

 is referred by Professor Osborn to the Pla- 

 giaulacidce. : but till it is proved to have 

 trenchant premolars it seems preferable to 

 place it provisionally in the present family. 

 Figure a in the accompanying woodcut gives 

 a side view of the type tooth, which has two 

 rows of tubercles separated by a longitudinal 

 groove ; the imperfect crown of another tooth 

 shown in b, and provisionally referred to the same genus, is remark- 

 able for the resemblance presented by its two remaining tubercles 

 to those of the teeth of Ornithorhynchus. The name Hypsiprym- 

 nopsis has been applied to a tooth of Microlestes, from the English 

 Rhsetic. 



Subclass II. Metatheria. — The members of this subclass agree 

 with the Prototheria in the structure of the brain and the presence 



Fig. 1 1 38. — a, Lateral view 

 of a tooth of Microlestes 

 antiquus ; b, Part of the crown 

 of a tooth on a still more en- 

 larged scale ; from the Upper 

 Trias of Wiirtemberg. (After 

 Lyell and Falconer.) 



