The Structure of Dinichthys 



165 



the line a~b is the axis of the condyle. As we know, it 

 must be placed exactly hori2;ontally in order not to pre' 

 vent the possibility of the head movement. Thus the 

 surface of ADL (c-d) was set at an angle of nearly 20° 

 to the vertical (e-d). In all the older reconstructions, it 

 was placed at a much larger angle. 



PosterO'DorsO'Lateral. — This (Text-figures 49, 

 50 and 55 PDL) is a large triangular plate, defining the 

 upper part of the hind margin of the body carapace. Its 

 hind margin is strongly thickened, but it gets thinner 

 toward the two other margins, where it is very thin. 

 On the outside the overlapping margins are very sharply 



Text-figure 48. 



The antero-dorso'lateral 



plate in front view. 



a-b, axis of condyle; c-d, surface 



of plate; e-d, vertical line; \d, 



condyle; );db, condyle basis; x, 



place where process on EB touches 



ADL. 



jT""^^ 



Text-figure 49. 

 The postero-dorso-lateral plate seen firom the outside. 



a-b, line of section shown in inset; x, cavity where spine-hke upper angle of PL fits 

 in; XII, anterior lateral canal. 



Text-figure 50. 

 Inside view of the postero-dorso- 

 lateral plate, showing the 

 groove, gr. 



