The Structure of Dinichthys 



147 



and triangular (Text-figure 27 V). The surface A, which is directed sideward, continues 

 gradually into the hind part of ASG (Text-figure 27 D). The surface B, which is directed 

 forward, is much larger. On its lower sharp-edged margin a second smaller pick is placed 

 (Text-figure 27 5). In the crevice between the two picks fits the big pick of the 

 infero-gnathal. 



In the middle of the tooth above the front edge (eg) is a big triangular impression 

 (Text-figure 27 C). Farther backward it forms the upper surface of the hind part of the 



Text-figure 27- 

 The antero-supra-gnathal plate of Dinichthys mtermedms Nwb. : I, from front; II, from edge; III, from side; 

 IV and V in sections indicated by lines on the figure. 



A, side surface; B, front surface; C, impression on top; D, hind thickened part; E, thin side portion on front part; eg, ed^; f, 



chief "pick"; s, secondary pick. 



tooth. This hind part (Text-figure 27 D) serves as an attachment to other plates and forms 

 a massive, long piece in approximate continuation of the pick of the tooth at an angle of 

 about 90° (Text-figure 27 III). Thus, in reality, the "tooth" is a massive, curved cuspidate 

 rod, with a thinner side part (Text-figure 27 £) where the secondary pick is placed. In 

 spite of the fact that this "tooth" was made only of bone, it must have served as a very 

 solid and effective weapon. 



Postero-Supra-Gnathal. — This plate (Text-figures 28 and 29 PSG], most com- 

 monly known under the name maxilla, is an oblong massive structure. Its hind margin 

 forms a sharp curved edge which is smooth and bright on the outside. On the 

 inside, a worn area also shows clearly how this tooth touches the infero-gnathal (Text- 

 figure 28 w). On the outside, PSG is divided into two parts — the real tooth (Text-figure 

 28 F) and the attached part (Text-figure 28 G), which is connected with the former at a 

 sharp angle. The real tooth is broadest in front (Text-figure 28 /) and narrower in the 

 hind part (Text-figure 28 h). Along the hind margin is a row of small tubercles. 



The front of the attached part continues into a long handle-like process (Text-figure 

 28 H). On the inside, this process is thickened and this thickening continues downward. 



