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Bashford Dean Memorial Volume 



direction, and continues onto the handle (Text-figures 21 and 23 X). There it gradually 

 approaches the lower margin and at last crosses it near the split. Another canal (Text- 

 figure 21 XI) runs parallel with the lower margin of SO, beginning at its hinder lower 

 corner (Text-figure 21 If). A little before it meets the above mentioned canal, it curves 

 sharply upward and fuses with the other. It is interesting to note that not in all Arthro- 

 dira do these two canals fuse. In Homostius, according to my investigations, they form 

 two separate canals. According to Dean (1909), the same is true in Titanichthys. 



On the inside, SO is formed in a more complicated manner. The thin hind part of 

 the blade is smooth also on this side. It bears the trace of an overlapping margin, which is 

 always to be found in the upper hind corner of SO (Text-figure 22 pso). This rather large 

 and round impression evidently indicates that there is another plate behind SO. On the 

 contrary, the fore part of the blade and the handle are strongly thickened. 



From the upper front corner of the blade (Text-figure 22 oh) begins a ridge (Text- 

 figures 22 and 23 Ri), which runs downward, at first very near the margin, later farther 



Text-figure 23. 

 The right sub-orbital plate of Dirtichtfiys intermedius Nwb. : I, from below; II, from above. The inset is a 



cross-section in the line a-b of Text-figure 21. 



A, real handle; a-h, line of section shown as an inset on Text-figure 21; B, tongue-shaped part of handle; c-d, section shown on 



inset; gr. groove on under side of tongue-shaped part; ip, impression between curving points of ridges Rj and R3; /jii, contact 



point with post-nasal plate; Pr, high crest on R^ ridge; R,,Rj,R3, R4, ridges on inside of SO; sp. split between real handle (A) and 



tongue-shaped part (B); y, curving point on ridge R; X, sub-post-orbital canal. 



