684 PLBOTOGNATHI. 



Oeder, V— PLECTOGNATHI, Cmier, 



Teleostean fishes with an incompletely ossified skeleton and few vertebrae. Gill-openings narrow, 

 situated in front of the pectoral fins : gills pectinate. Head often large. Mouth narrow : the bones of the 

 upper jaw mostly united, sometimes produced into the form of a beak. Teeth may be distinct in the jaws or 

 absent. There may be a single soft-rayed dorsal fin belonging to the caudal portion of the vertebral column, 

 and situated opposite the anal : while in some a rudimentary spinous dorsal is also present : ventrals, when 

 existing, in the form of spines. Skin either smooth, or with rough scales, or ossified in the form of plates or 

 spines. Air-vessel destitute of a pneumatic duct. 



Geographical d/istribution. — ^Mostly oceanic, but some are found in large rivers, and many in estuaries 

 and tidal pieces of water in temperate and tropical portions of tlie globe. 



SYNOPSIS OP FAMILIES. 



1. Selerodermi. Distinct teeth in the jaws. 



2. Gynmodontes. Jaws modified into a beak. 



Family, I— SCLERODEEMI, Cmier. 



Body compressed or angular : snout somewhat produced. Distinct teeth in small numbers in the 

 jaws. A barbel in one genus. The elements of a spinous dorsal and ventral fins generally present, but 

 variously modified. Skin rough or spinate, or the scales in the form of a firm carapace. 



Geographical distribution. — ^Marine fishes found in tropical and temperate regions. 



SYNOPSIS OP INDIAN GENERA. 



First group — Teiacanthina. 



Body compressed : dermal covering in the form of small, rough, scale-like scutes. A spinous dorsal 

 with from 4 to 6 spines : a pair of strong ventral spines articulated to the pelvic bones. 



1. Triacamihms. Outer row of teeth cutting, p. 684. 



Second group — Balistina. 



Body compressed : dermal covering rough, or with movable scutes. Spinous dorsal with from 1 to 

 3 spines : ventrals, if present, consisting of a single pelvic projection. 



2. Balistes. Three dorsal spines : no barbels, p. 686. 



3. Monacanthus. One or two dorsal spines : no barbels, p. 692. 



4. Anacanthus. A barbel present, p. 694. 



Third group— Osteaciontina. 

 Body angular with the dermal covering forming a carapace, leaving the snout and bases of the fins 

 covered by skin. Spinous dorsal and ventral fins absent, except in the form of osseous protuberances. 



5. Ostraoion. Teeth small, slender and in a single row. Carapace closed behind the anal fin, p. 695. 



First group — Teiacanthina. 

 Body compressed : dermal covering in the form of small, rough, scale-like scutes. A spinous dorsal 

 with from 4 to 6 spines : a pair of strong ventral spines, articulated to the pelvic bones. 



Genus, 1 — Tbiacanthus, Guvier. 

 Body oblong, compressed, ending in a somewhat elongated caudal portion. Eyes lateral, high up, situated 

 near the hmd edge of head. Teeth m two rows in both jaws, the outer 10 im, rmmber, being incisor-like : the inner, 

 from 2 to 4, being more molariform. First dorsal fin consisting of a long and strong spine, followed by from 3 to 

 5 smaller and weak ones : ventrals formed hy a pair of strong spines articulated by a joint or ossified to the pelvic 

 bones : caudal lobed. Scales minute and rough. Lateral-line present. Air-vessel strong. 



