The Structure of Dinichthys 125 



Moreover, the latter nomenclature is very common and has been used in more than one 

 hundred papers on the Arthrodira. 



In this work, the English'American nomenclature will be applied with a slight altera' 

 tion, so that the names will not remind one of the bone names of the fishes. This 

 nomenclature has been worked out by Professor J. E. Hyde of Cleveland and the present 

 writer. It will be used by Professor Hyde in his series of monographic descriptions of the 

 Arthrodiran material from the Cleveland shale. This new nomenclature is shown below. 

 The abbreviations used in this work are placed in parentheses; the numbers refer to the 

 various plates shown in the drawings (Text-figures 9, 10, and 11). 



NOMENCLATURE OF THE PLATES IN THE ARTHRODIRA 



PosterO'Supra-Gnathal (PSG) 

 Antero'Supra-Gnathal (ASG) 



Body Carapace 

 Median-Dorsal (MD) 

 Antero-Dorso-Lateral (ADL) 

 Postero-Dorso-Lateral (PDL) 

 Antero-Lateral (AL) 

 Postero-Lateral (PL) 

 Spinal (Sp) 

 Intero-Lateral (IL) 

 Antero-Ventro-Lateral (AVL) 

 Postero-Ventro-Lateral (PVL) 

 Antero-Median- Ventral (AMV) 

 Median- Ventral (MV) 

 As can be seen, the alterations are not great. The name ''occipital,'' used for cranial 

 bones of other animals, is replaced by the more neutral name basal. The little plate. No. 7, 

 is called post-marginal, being behind the marginal. This plate has been called ''angular" 

 by Traquair (1894) and Heintz (1930.2) — an unsuitable name because the plate has nothing 

 to do with the "angular" in the fishes. Jaekel (1902) called it "Supra-temporale." 



The name post-sub-orbital is given to a plate which has had many names before. 

 Pander (1857) called it "Opercul"; Newberry (1889) called it "post-maxiUary"; Dean 

 (1895), "hyomandibular"; Woodward (1898), "operculum"; Traquair (1889), ''jugal 

 or post-maxillary"; and Jaekel (1902), "Quadra to-jugale." 



The post-nasal is a small plate in front of the head and surrounds the nasal open- 

 ing. Traquair (1889) calls this the "pre-maxilla"; and Jaekel (1902) once refers to it as 

 the "Lacrymale," and later (1906.1) calls it the "Post-nasale." 



The jaw elements have the names Hussakof proposed in 1906, instead of maxillary, 

 pre-maxillary and mandible, all names well known from the fishes. Plate No. 14 is called 

 postero-infero-gnathal. Jaekel called this plate the "Articulate" in Pholidosteus. 



