The Structure of Dinichthys 



123 



Text-figure 9. 

 The head armor of the "Ideal Arthrodire" with the plates separated. 



Plates: 1, median-basal (MB); 2, cxterno-basal (EB); 3, central (C); 4, marginal (M); 5, post-orbital (PtO); 6, pre-orbital 

 (PtO); 7, post-marginal (PM); 8, pineal (P); 9, rostral (R), 10, sub-orbital (S0)\ U, post-sub-orbital (PsO); 12, post-nasal 

 (PK); IJ, infero-gnathal (IG); 14, postero-infero gnathal (PIG); 15, postero-supra-gnathal (PSG); 16, antero-supra-gnathal (ASG)_ 

 Canals: I, pre-orbital (Proc); II, III, IX, X, sub-post-orbital {Sptoc); IV, VI, VII, marginal (Mc); V, post-marginal (Pmc); 



VIII, externo-basal (Ebc); XI, gnathal (Gjic). 



It is possible that later investigations will show that in the Arthrodira the head 

 shield included some more plates. Nevertheless I am quite sure that the picture of this 

 Arthrodiran head will not be altered in any particular way.- 



As we see, the head contains 37 single plates (Text'figure 9). Among them are 3 

 symmetrically placed in the median line, while 34 others form 17 pairs of unsymmetrical 

 side plates (right and left). The body carapace has only 19 plates; 3 symmetrical median 

 plates, and 8 pairs of unsymmetrical side plates (Text-figures 10 and 11). Thus the whole 

 carapace of the ''ideal arthrodire" is built of 56 single plates (6 unpaired and 25 paired). 



- This supposition proves to be correct. The author has been convinced that Professor Hyde has found four new plates in the 

 head of Dinichthys. Nevertheless, the picture of the whole head is not changed. These four new plates will be described in Pro- 

 fessor Hyde's monograph on Dinichthys. . 



