DEVONIC FISHES OF TIIE NEW YORK FORMATIONS II9 



Adopting for our thesis the obvious fact that Dinichthys and Cocco- 

 steus are constructed upon the same general type, we may now take note of 

 such differences as exist between them, other than mere size ; and for 

 immediate purpose of comparison it will be convenient to choose D. 

 herzeri, D. terrelli and D. i n t e r m e d i u s as representatives of 

 the former, and C. d e c i p i e n s as representative of the latter genus. 

 First, as to the abdominal armor. Here we observe a perfect correspond- 

 ence throughout, both as to number, arrangement and general form of the 

 plates [cf. text fig. 23]. The dorsomedian of Dinichthys is relatively shorter 

 than that of Coccosteus, more emarginate in front and rounded behind, and 

 its inferior keel is developed into a stout terminal process. There are not 

 usually traces of sensory canals upon its external surface. In Coccosteus, 

 the anterolateral is bounded in front and below by a distinct plate, the 

 interlateral, which forms the connection between the dorsolateral and ventral 

 portions of the abdominal armor. In Dinichthys, the interlateral does not 

 occur as a distinct plate, but may be represented by the forklike prolonga- 

 tion of the so called "clavicular," the broad upper portion of which cor- 

 responds, of course, to the anterolateral. The median ventrals of Cocco- 

 steus are always separate ; in Dinichthys they are occasionally fused. 



Secondly, as to the head shield. Again there is notable correspondence 

 of plate for plate, and in the arrangement of sensory canals. The bones 

 are more intimately fused in Dinichthys than in Coccosteus, and the sutures 

 are less wavy. The median occipital is generally pointed in front [^cf. text 

 fig. 23], the pineal plate is lancet-shaped and produced backward so as to 

 come in contact with both the centrals and preorbitals, instead of being 

 inclosed by the latter alone, and the plates forming the sides of the head 

 shield are narrower than in Coccosteus. None of these differences, how- 

 ever, can be considered other than of secondary importance, and their aggre- 

 gate does not in the least obscure identity of structural plan common to 

 both genera. The imaginary plate interpreted by Newberry' with some 



' Newberry J. S. U. S. Geol. Sur. Monogr. 1889. 16:334, pi. 52, fig. 2. 



