VEETEBEATES. 19 



highly ornamented ones of the "Old Red," seems to he quite sufficient, though 

 both had been long considered but species of the genus Iloloptychius. The 

 Devonian Holoptychii are well known by the discovery of numerous nearly 

 entire individuals, in which scales, fins and bones are almost uninjured and 

 unmoved; but the so-called Holoptychii of the Coal Measures are, as yet, only 

 represented in collections by the large, thin scales which have been referred to, 

 by numerous large, detached teeth, having fluted bases and a lenticular section, 

 and by massive bony jaws, bearing these teeth and numerous intermediate and 

 smaller ones. 



In Ohio, what seem to be fragments of several species of Rhizodus have been 

 discovered, by one of the authors, consisting of large, thin, quadrate, reticulated 

 scales, numerous detached flattened teeth, and portions of jaws bearing teeth. 

 In these jaws he observed that there are but a few of the large teeth with cut- 

 ting edges, the spaces between them being occupied by much smaller teeth, 

 having similar fluted bases, but with a circular section throughout. 



Rhizodus occidentalis, N. and W. 



Fig. 2. 



Rhizodus, occidentalis. 



Scales thin, rotundato-quadrate or sub-triangular in outline, 

 li inches in diameter; anterior margin rounded; posterior scol- 

 loped; exterior surface unknown; interior marked with concen- 

 tric wavy lines of growth, and, near the margin, very finely and 

 beautifully striated. 



This scale is the only representative, so far as our knowledge extends, of the 

 genus Rhizodus yet found in the rocks of Illinois. As the scales and teeth of 



