FISHES. 



287 



group has been distinguished as an order — Plectognathi. The real anatomical 

 characters, however, are very slight, and in many, or rather most, respects, they sub- 

 stantially agree with those of the Teleocephali ; but the elements of the lower jaw are 

 coalesced into single pieces answering to the two rami; the supramaxillary and 

 intermaxillary bones are also generally united (and it is in allusion to this that the 

 name Plectognathi has been given), and the scapular arch is connected by suture with 

 the cranium. 



SuB-ObDEE I. — SCLEKODERMI. 



The Scleroderms are the most generalized of the Plectognaths, and those least 

 aberrant in external appearance as well as anatomical characters. They are, in brief, 



Fig. 161. — Phyllopieryx eques. 



Plectognaths with a spinous dorsal (often reduced to a single spine) just behind or 

 over the cranium ; of a normal, fish-like form, covered with scales of regular form, or 

 more or less spiniferous or spiniform, and with distinct teeth in the jaws. 



The species which exhibit the nearest relation to any of the typical fishes are cer- 

 tain forms found in the East Indian and Cuban seas. These form the family Tkiacan- 

 THiD^. They manifest some relationship to the fishes that have been previously 

 considered among the Teleocephali under the heading Teuthidoidea (p. 211). 



The Triacanthidae have a compi-essed body, covered with scales not unlike those of 

 typical fishes, two dorsals, the first having several spines, and two large ventral 

 spines, but no soft rays. Inasmuch as the only special interest of the family is the 

 manifestation of the relationship of the order, we pass at once to a better-known 

 group. 



A prominent form in tropical seas is that which has been distinguished as the 

 family Balistid^. These are compressed fishes with scales either of a rhomboid 



