DEVONIC FISHES OF THE NEW YORK FORMATIONS 



45 



The orbital opening \_o'] is, as already mentioned, small compared with 

 that of Asterolepis, and, moreover, its anterior margin shows scarcely any 

 reentering flexure. Its right and left portions are almost completely filled 

 by a system of sclerotic plates, the two inner ones being very considerably 

 larger than the two outer, and the middle portion is covered by two loosely 

 attached plates, namely the median or pineal \_m~\, and a very narrow 

 T-shaped plate x (called by Patten the " ethmoid ") close in front of it. 

 From the center of this narrow plate, as shown by Whiteaves and con- 

 firmed by Patten, a small linear process with expanded lower extremity 

 passes down perpendicularly into the interior of the head, almost reaching 

 a thin transverse shelf of bone which projects downwards from the under 

 side of the premedian [/. »«.] The space thus partitioned off beneath the 

 premedian is interpreted by Patten as an " olfactory chamber," and certain 

 conjectures are hazarded by him as to the course of the olfactory nerves, 

 which will be referred to presently. The median plate of the ocular open- 

 ing is nearly perforated by a deep pineal foramen, similar to that occurring 

 in Pterichthys, and often indicated by a low tubercle on the external sur- 

 face. Two other pits, shallower than the first and without any external 

 indications of their presence, are symmetrically placed behind it on the 

 under side of the small postmedian plate. The unpaired pit is in all prob- 

 ability to be regarded as the impression of the pineal body, but it is difficult 

 to imagine what may have been the function of the posterior pair. Analogy 

 with all other vertebrates does not permit us to entertain the suggestion, 

 put forward with some confidence by Professor Patten, that these three pits 

 are of similar nature and indicate the presence of a triocular median eye." 



A matter of absorbing interest is the arrangement of mouth parts in 

 this species, now very satisfactorily known. Beneath the head shield at its 

 front extremity [text fig. 1 1 mx] there is observed a pair of thin, concave 

 plates of bone with free median and posterior margins, the latter being 

 sharply beveled and serrated. These plates are quite similar to those 

 called the maxillae in Pterichthys [text fig. 8 mx~\, but are less extensively 



'New Facts Concerning Bothriolepis. Biol. Bui. 1904. 7; 121. 



