285 



Anterior outer within the border, oval, on n 

 high tuberosity; beak long, narrow ; max- 

 illary areas large /. eoccenus. 



Anterior outer oval, standing on a high tube- 

 rosity ; maxillary areas small ; beak nar- 

 row - ■ /. monolophus. 



Anterior outer oval, much within the' border, 



on a low tuberosity ; beak thick, long /. incrassatus. 



Anterior outer oval, not on a tuberosity ; pos- 

 terior outer minute /. gaskittii. 



BB. Anterior outer area not produced anterior to the 

 border of the inner area: 



Anterior outer moderate, on a prominent angle 

 of outer margin; inner margin abruptly 

 excavated from inner area, which is wide. /. fecundus. 



Anterior outer area not standing on an angle ; 

 inner border not abruptly excavated; inner 

 area narrowed, not produced beyond ante- 

 rior outer - - /. mirificus. 



Anterior outer area not on a projection, not ex- 

 tending as far as inner, which is narrow ; 

 beak long, straight - . /. miersii. 



Exterior areas very small, the anterior not on an 

 elevation ; beak not excavated, but turned 

 outward ; inner area very wide . /. divaricatus. 



Isciiyodus stenobeyus, Cope. 



Indicated by both rami of the mandibular arch. The characters are 

 striking. The outer border rises rapidly from a little behind the apex, first 

 to a shoulder, which supports the first exterior dentinal area, and then steeply 

 to an oblicpie border, which bears the posterior area. The inner masticatory 

 margin remains parallel with the inferior border of the jaw, marking one- 

 third the total depth. The external areas are very narrow, and behind the 

 anterior a smaller one appears in the position of the inner one of I. tripar- 

 titus, thus representing the outer part of the large inner area. The inner 

 part of this area appears on the inner edge, far removed from the former, is 



