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Bashford Dean hiemorial Volume 



With that exception, it has 

 hitherto only been known 

 in Dinomyhstoma (Eastman 

 1906.1). 



No changes have been 

 made in the names of the 

 plates of the body carapace. 



Finally, let us consider 

 the sensory canals. These 

 canals in the Arthrodira 

 show the same constancy 

 as the plates. We find the 

 same fundamental plan of ar' 

 rangement in all the forms.' 

 Different authors have pro' 

 posed different names for 

 these canals, but most fre^ 

 quently they have been 

 named from the plates on 

 which they were situated. 

 The most detailed nomen^ 

 clature has been proposed 

 by Claypole (1892.2) and 

 Stensio (1925). Stensio's 

 nomenclature is based on a 

 comparison of the course of the sensory canals of the Arthrodira with that in Mdcro' 

 petalkhthys and other fishes. He suggests calling them by the names used for other fishes. 



The present writer prefers the more neutral names shown in the following table in 

 which the abbreviations are placed in parentheses; the numbers relate to the different 

 canals on the drawing (Text-figure 9). 



NOMENCLATURE OF THE SENSORY CANALS IN THE ARTHRODIRA 



Text-figure 11. 

 The ventral shield of the "Ideal Arthrodire" with plates separated. 



Plates: 22, spinal (Sp); 23, intero-Iateral (IL); 24, antero-ventro-lateral (AVL); 

 25, postero-ventro-Iateral (PVL); 26, antero-median-ventral (AMV); 27, median- 

 ventral (MV). 

 Canals: XV, ventral canal (Vc). 



I. Pre-orbital canal (Proc) 



III.V Sub-post-orbital canal (Sptoc) 

 IX.( 



IV.| 



VI. / Marginal canal (Mc) 

 VII.' 



V. Post-marginal canal (Pmc) 



VIII. Externo-basal canal (Ebc) 



XI. Gnathal canal (Gnc) 



XII. Anterior sensory canal (Aslc) 



XIII. Posterior sensory canal (Pslc) 



XIV. Dorsal canal (Dc) 

 XV. Ventral canal (Vc) 



3 In one form of Acanthaspida from Germany (Lunaspis), described by Broili (1929), it was impossible to indicate any sensory 

 canals despite the very well preserved material. 



