PLECTOGNATHI. 277 



PLECTOGNATHI. 



The sixth order of osseous fish makes a near approach to the Chondropterygii in 

 the imperfection of the jaws and the tardy ossification of the skeleton, which is 

 nevertheless fibrous, and in its general structure the same as in ordinary fishes. 

 Their principal distinctive character consists in the labials being joined immove- 

 ably to the intermaxillaries which form the upper jaw, and in the arch of the palate 

 being united by suture to the cranium, and consequently destitute of all motion. 

 The gill-covers and rays are moreover concealed under a thick skin which leaves 

 only a small branchial slit ; there are no ribs ; the true ventrals are wanting, the 

 alimentary canal is wide, without caeca, and an air-bladder of considerable size is 

 almost always present. The order comprises two very natural families, the Gym- 

 nodontes, which, instead of teeth, have their jaws armed with a substance like 

 ivory, divided internally into plates, and having a general resemblance to the beak 

 of a parrot ; and Sclerodermata, which are readily known by a conical or pyra- 

 midal snout projecting from before the eyes, and terminated by a small mouth armed 

 with a few distinct teeth in each jaw. Their skin is generally rough, or clothed 

 with hard scales *. The following species have been stated to frequent the coasts 

 of the United States : — Dlodon punctatus, Cuvier (jD. attinga, Schoepf, I). 

 hystrix, Bl.) ; D. rivulatus, Cuvier (D. maculato-striatus, Mitchill) ; D. 

 pilosus, Mitchill ; Tetraodon geometricus, Schneider Bl. ; T. lineatus, Bl., 

 Schoepf ; T. hispidus, Schoepf ; T. turgidus, Mitchill ; T. Icevigatus, 

 Willough., Schn. Bl. ; T. curvus, Mitchill ; Orthagoriscus mola, Schn. 

 (Tetraodon mola, Linn., Schoepf); Balistes tomentosus, Linn.; B. vetula, 

 Bl. ; B. hispidus, Linn., Schn. Bl. ; B. monoceros, Linn., Penn. (Aleuteres 

 monoceros, Smith) ; B. aurantiacus, Smith; B. broccus, Smith; B. suffiamen, 

 Smith ; Ostracion triqueter, Smith ; O. bicaudalis, Smith ; 0. quadricornis, 

 Schn., Bl. There is considerable confusion in the application of these names, 

 some of them, at least, being preoccupied by fish belonging to other quarters of the 

 ocean. 



* The P/ectoynathi are included by M. Aga'-siz among his Ganoulians. 



