1696 Bulletin 47, United States National Mnsenm. 



profusely covered with fine darker punctnlations ; fins all pale orange. 

 (Description from Valenciennes's plate, which may incorrectly represent 

 Xesnrxis imnctatns.). Galapagos Islands; only the type known, {latus 

 side; clavis, stripe.) 



Prionurus latielavius, Valenciennes, Voyage Venus, 335, pi. 7, Ar. 2, 184C,, Galapagos 

 Islands; GiJNTHER, Cat., in, 347, 1861. 



Group PLECTOGNATHI. 

 (The Plectognathous Fishes.) 



One of the most important offshoots of the Acanihopteri is the group or 

 order Plectognathi, including the 3 suborders of Sclerodermi, Osfracodermi 

 and Gymnodontes. The extremes of this group show a remarkable diver- 

 gence from the usual type of spiny-rayed fishes. The more generalized 

 forms are, however, very close to the group called Squamijniines, and espe- 

 cially to the family of Tcuthidido'. There can be no doubt of the common 

 origin of Balistidff and Tcitthididw and that the divergence is comparatively 

 recent. The close connection of these groups leads us to subordinate tbe 

 Plectognathi to the Acanthopieri and to place its 3 suborders in their natural 

 position as an offshoot from the Squamipinnes. The PJectoynathi may be 

 thus defined : * 



Scapula suspended to the cranium by a post-temporal which is short, 

 undivided, and auchylosed to the epiotic. Preniaxillaries usually coosified 

 with the maxillaries behind and the dentary bones witli the articular; 

 interopercle a slender rod ; lower pharyngeal bones distiuct ; upper pharyn- 

 geals laminar, usually vertical and transverse; skin usuiilly with rough 

 shields or scales or bony plates; "skeleton imperfectly ossified, the number 

 of vertebra' usually small, typically less than 24 (usually 14 to 20) ; rarely 

 considerably increased. Gill-opeuiugs restricted to the sides; ventral fins 

 reduced or wanting, the pelvic bones usually elongate. Spinous dorsal 

 small or wanting ; air bladder without duct. Fishes chiefly of the tropics, 

 mostly inactive and depending on their tough skin or bony or spinous 

 armature for their protection. (^rAexroj, braided or joined; yvdOoi, jaw.) 



Suliorders of Plectognathi. 



a. Jaws -with distinct teetli. 



h. Spinous dorsal present; body with scales ormovable plates . Sclerodermi. 



bb. Spinous dorsal wanting; body encased in an immovable carapace of hexagonal 



plates; the jaws, bases of flns, and tail only free. Ostracodermi. 



aa. J.aws each modified into a sort of beak; each jaw with an enamel-like covering and 



without distinct teeth ; scales rhomboid or spiniform, with root-like insertions; 



spinous dorsal wanting. Gymnodontes. 



' The definition of this group is taken from Dr. Gill. (Proc. U .'S. Nat. Mua. 1884, 412.) 



