362 



rROCEEDINQS OP THE ACADEMY OP 



MICEOCONODON. 



[1886. 



Microconodon tenuirostris, gen. et sp. nov. 



This genus is founded upon the specimen in the collection of 

 the Academy of Natural Sciences of Philadelphia, which was 

 described by Emmons as Dromatherium. 



Generic Characters. A wide diastema between the canine 

 and first premolar. Molars and premolars unlike. Premolars 

 simple, erect cones with a faint posterior cinguliim and partly 

 bi-fanged. Molars bi-fanged with broad crowns supporting a large 

 median cusp, at the sides of which are anterior and posterior 

 conical cusps, sub-equal in size, and a distinct posterior cinguliim. 



The ramus is about two-thirds the length of that of Droma- 

 therium. Its general lower curvature is single. There is a de- 

 pression extending beneath the molar-premolar series, but this is 

 shallower than the mylohyoid groove, and I infer that the outer 



Microconodon tenuirostris Osb. Magnified. 



surface of the jaw is the one exposed. The coronoid rises by a 

 gentle curvature above the molars and the fractured portion seems 

 to have left a faint impression on the matrix, which indicates a 

 low rounded contour. The posterior half of the lower border is 

 marked by a downward process, somewhat similar to that in 

 Peramus. The surface of the process bears a shallow fossa. 

 Above this the crotaphyte fossa is faintly marked. The sym- 

 physial portion of the jaw is partly fractured. The matrix bears 

 an impression which may have been left by a tooth, but more 

 probably is accidental. Altogether, the delicate character of this 

 ramus indicates an animal of feebler masticating power than Dro- 

 matherium. 



The molars probably extended backward to the rise of the 

 upper border. If so, the molar-premolar series covered a greater 

 proportional space than those of Dromatherium. This arose 

 from the comparatively broader crow^ns of the molars. By 

 analogy with several other Mesozoic genera, we may suppose 

 that the foremost molar preserved is the second, and that behind 



