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Bashford Dean Memorial Volume 



Text-figure 10. 

 The dorsal shield of the "Ideal Arthrodire" with bones separated 



Plates: 17, median-dorsal (MD); 18, antero-dorsal-lateral (ADL); 19, postero-dorso-lateral {PDL); 20, antero-lateral (AL); 



21, postero-lateral (PL); 22, spinal (Sp); 23, intero-lateral (IL). 

 Canals: XII, anterior lateral (AsIc); XIII, posterior lateral (Pslc); XIV dorsal (Dc). 



The nomenclature of the single plates in the carapace ot an Arthrodire is very varied 

 according to the different writers. In the works of Dean (1901) and Heintz (1929.1) are 

 found tables giving the names used by various authors. 



It is usually acknowledged that a mistake is made in calling the different plates in the 

 Arthrodire armor by the same names given to the bones in the cranium and shoulder 

 girdle of the fishes. The Arthrodira are so isolated in theif systematic position that the 

 homology between their carapace plates and the cranial bones of the fishes is too un- 

 certain. Therefore it is better to change such names as "frontal," "parietal," "occipital," 

 "quadratum," "mandible," etc., especially used in Germany by Jaekel, to more neutral 

 names. For this reason, the names given to Arthrodiran plates in England and America 

 are the best. They are based on the position of the plates in the carapace and are there' 

 fore more neutral (e.g., pre-orbital, central, median-dorsal, antero'ventro-lateral, etc.). 



In 1925, Stensio proposed naming the single plates of the Arthrodiran head with 

 capital letters, as B. M, M2, L, P, etc. This method of nomenclature, notwithstanding its 

 many advantages, is, in my opinion, unsatisfactory. The single letters give no character' 

 istic of the plate's position or relation to other plates, as do the English' American names. 



