36 KEVV YORK STATE MUSEUM 



shield is one of larger size and somewhat quadrate shape, the premedian 

 [/. ;«.]. Two large paired pieces, the lateral plates [/], one on each side, 

 bound the median opening laterally, and also extend to the front of the 

 shield, behind which, and forming part of the hinder margin of the buckler 

 external to the median occipital, are two other paired plates, the lateral 

 occipital [/. ^rr.] and the angular [a^]. 



The upper and lateral aspect of the cranial shield is now completed by 

 a plate on each side, which is only loosely articulated in Asterolepis and 

 Pterichthys, though firmly sutured in Bothriolepis. This is the extralateral 

 [r. /.] or opercular plate, as it has also been called by some writers. 



On the lower aspect of the head and close behind the anterior margin 

 of the shield are two transversely oblong plates [w.i".], right and left, the 

 position of which was first determined by Whiteaves in Bothriolepis,' an 

 observation corroborated by Smith Woodward.'' These plates must have 

 been situated in front of the mouth, and may therefore be termed, at least 

 conventionally, as maxillae. There can be no doubt that they were simi- 

 larly placed in Pterichth)'s ("mental plates"), and in Asterolepis they were 

 designated ))iaxiUac infcriorcs by Pander. Close to the postero-external 

 angle of each of these plates there is a rounded notch, considered by Smith 

 Woodward in Bothriolepis as possibly indicating a nasal opening.^ 



The anterior part of the trunk is incased in a boxlike armoring, nearly 

 flat below, and vaulted above. It is composed of 13 plates, of which 3 are 

 median and 10 paired, and these are united with one another by overlapping 

 sutures, a marginal band along the internal surface of the overlapping plate 

 being excavated to fit on to a correspondingly excavated band along the 

 margin of the outer surface of the plate overlapped. 



On the upper surface we see the anterior and posterior median dorsal 



'Roy. Soc. Can. Trans. 1887. v. 4, § 4, p. 103, 104. 



^Geol. Mag. Dec. 3, 1892. 9: 484. 



3 This notch is somewhat differently placed in Bothriolepis, being fair on the outer 

 margin of the plate instead of at its postero-external angle. Patten interprets the plates 

 here called maxillae as mandibles. 



