1696 Bulletin 4.7, United States National Museum. 



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

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

 Xesurus punctatus.). Galapagos Islands; only the type known, (latus 

 side; clavis, stripe.) 



Prionurus laticlavius, VALENCIENNES, Voyage Venus, 335, pi. 7, fig. 2, 3846, Galapagos 

 Islands; GUNTHER, Cat., m, 347, 1861. 



Group PLECTOGNATHI. 



(THE PLECTOaNATHOUS FlSHES.) 



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

 order Plectognathi, including the 3 suborders of Sclerodermi, Ostracodermi 

 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 Squamipinnes, and espe- 

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

 origin of Balistidce and Teiitliididce and that the divergence is comparatively 

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

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

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

 thus defined : * 



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

 undivided, and anchylosed to the epiotic. Premaxillaries usually coosified 

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

 interopercle a slender rod ; lower pharyngeal bones distinct ; upper pharyii- 

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

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

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

 considerably increased. Gill-openings 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. (Tt\EHr6^ braided or joined; yvdftos, jaw.) 



Suborders of PLECTOGNATHI. 



a. Jaws with distinct teeth. 



b. Spinous dorsal present; body with scales or movable plates. SCLERODERMI. 



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



plates; the jaws, bases of fins, and tail only free. OSTRACODERMI. 



aa. Jaws 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. Mus. 1884, 412.) 



