DEVONIC FISHES OF THE NEW YORK FORMATIONS 



35 



closed above, below, and at the sides, but open in front for the head, and 

 behind for the tail. The head is covered almost entirely by a dorsal 

 shield, formed also of plates united by suture. The two pectoral limbs 

 consist also of plates similarly united, and are internally hollow so far as 

 their remains in the stone are concerned. 



The head shield [text fig. 7] is semielliptical in shape, rounded in 

 front and truncated behind, where it joins the system of body plates. In 

 the center it shows a transverse aperture, the median opening or orbit, 

 slightly contracted in the middle and expanded at each of its rounded sides. 

 This opening is in perfect specimens filled up by at least three other plates, 



Fig. 9 Restored outline of Ptericlithys milleri Agassiz; lateral aspect, x ^ (After Traquair) 



which, being loose, are usually lost. Of these, one is in the center, quad- 

 rate in shape, but with concave outer margins, and may be called the 

 median or pineal plate \jn], as it shows on the internal aspect a shallow 

 rounded pit, pointed out by Dr Smith Woodward as probably the impres- 

 sion of the pineal body. This is by its outer concave margins in contact 

 on each side with a rounded convex ocular plate [0], indicating certainly 

 the position of the eye, but whether or not due to an ossification in the 

 sclerotic is doubtful. [In Bothriolepis the orbits have two sclerotic plates 

 each.] The nuchal region is occupied by a large plate, the median occi- 

 pital [ffi. occ.\ shaped something like the conventional royal " crown," but 

 without the pinnacle in the center. In front of this and immediately behind 

 the median opening is a smaller plate, the postmedian [/A m7\ ; while 

 between the anterior margin of that opening and the front of the cranial 



