VERTEBRATES. 349 



The specimen of Amblypterus before us, though so imperfect, shows some 

 points in the structure and habits of the genus which have been long misun- 

 derstood. Agassiz says of the dentition of Amblypterus, that the teeth are en 

 brosse, and hence it was a vegetable eater ; but in these specimens the mandi- 

 bles are distinctly shown, bearing on the outer edge of each a row of relatively 

 large and acute teeth, such as could only be intended for the use of a carnivore. 

 Probably, as in analagous fishes, the jaw bore smaller teeth within, but the 

 large ones are as distinct, and relatively as large as those of Lepidosteus. The 

 dentition is even better shown in some specimens of Amblypterus from Saar- 

 bruck in the possession of one of the authors, and these exhibit precisely the 

 character described above. 



GENUS RHIZODUS, Owen. 

 RHIZODUS RETICULATUS, N. and W. 



PI. iii, fig. 9, 13, 14. 



SCALES of large size, oblong or oval in outline, anterior ex- 

 tremity somewhat pointed, posterior end truncated; margins 

 bordered by a distinct radiate-striated band, broadest on the 

 anterior and posterior extremities, and marked by numerous 

 imperfectly parallel and concentric plications or lines of growth ; 

 under surface nearly smooth, with a subcentral tubercle ; up- 

 per surface, within the marginal band, covered with an irre- 

 gular reticulation of raised lines, which enclose elongated poly- 

 gonal areolae ; on the exposed anterior third of the scale, these 

 lines are more or less broken into rows of minute tubercles. 



The elongated form of these scales is their most striking character. This is 

 best shown in some of the smaller specimens, which are more than twice as 

 long as broad, and spatulate in outline. The largest ones are two and a-half 

 inches long by one and one-quarter broad. The scale is thin, and the orna. 

 mentation delicate, similar in style to that of R. occidentals, but less strong. 

 In that species, the scale is much more rounded, the two diameters being nearly 

 equal. 



Formation and locality : Coal Measures ; Mazon creek, Grundy county, 111. 



