1903.] ii<^yi North American Cretaceous Fishes. 39 



The articulation of the lower jaw is "below the hinder half 

 of the orbit. The articular sends up a strong hook-like pro- 

 cess behind the quadrate. The maxilla is curved and does 

 not extend back as far as to the quadrate. Neither the 

 maxilla nor the mandible appears to have differed much from 

 those of Thryptodns zitteli. The mouth has been relatively 

 small and quite oblique. 



The structure of the greater portion of the dental apparatus 

 was unknown to Cope. He states that teeth are found on 

 the ethmoid bone, his united premaxillae; but the present 

 writer has been able to find there only a slight roughness. 

 When the fish died, the mouth was left in a gaping position. 

 Recently the matrix has been removed from it to a depth of 

 98 mm. from the edge of the vomer. This reveals the fact 

 that the mouth is armed with large bony plates which closely 

 resemble those described by Loomis ^-".^^_,„„.,^^ 



as belonging to Thryptodus . From a /^'S!^^!^ 



gelatine mold, plaster casts have been F'^o^iB'^^^^^ 



made of the upper surface of the /!, ,, ■ .,,,..^ , '"A 



mouth and of the floor. These have / ' ', / 



given much assistance to the artist 

 in making drawings of the parts. The 

 excavation of the cavity of the mouth 

 did not extend quite to the hinder 

 end of the plates, but must have ap- 

 proached them closely. In the front i'ti;^ I %;x%v ifc.-- • i •; 

 of the mouth we find a short, broad :; \ ^|^ Ic^ • / 



vomer (Fig. 24, z;ow.) which is covered \ l!&>^ W ' 



with villiform teeth. Behind this is ''■— 



found a dental plate (par.) at least s^ V,J:::rl:'F^1^''^. 

 82 mm. long and about 30 mm. wide. ^^l^l^^-^Tr/X'^t!^^^^^ 

 It has nearly parallel sides, and the '"""- ^°'""- 

 lower surface is concave. The concavity is greatest just 

 behind the middle. No doubt, this plate rests on the par- 

 asphenoidal bone, as in A. javirostris. On each side of this 

 parasphenoidal plate and articulating closely with it is another 

 plate {pal.), long, narrow in front, broadening behind, and 

 convex in cross-section. These plates represent the palatine 



