PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 411 



SYNOPSIS OF THE PLECTOGNATH FISHES. 

 By THEOnORJE Ollil.. 



By common consent the fishes combined by Ouvier in 1817 under 

 the ordinal designation Plectognathes have been retained as an order. 

 Nevertheless, objection has been made against it by several ichthyolo- 

 gists, and it may be regarded as still an open question whether th^ group 

 is entitled to ordinal distinction. In the latest general work on sys- 

 tematic ichthyology,* the " sixth order, Plectognathi," is thus character- 

 ized : 



"Teleosteoiis fishes, with rough scales, or with ossifications of the 

 cutis in the form of scutes or spines; skin sometimes entirely naked. 

 Skeleton incompletely ossified, with the vertebrae in small number. 

 Gills pectinate; a narrow gill opening in front of the pectoral fins. 

 Mouth narrow ; the bones of the upper jaw generally firmly united. 

 A soft dorsal, belonging to the caudal portion of the vertebral column, 

 opposite to the anal ; sometimes elements of a spinous dorsal besides. 

 Ventral fins, none, or reduced to si^ines. Air-bladder without pneu- 

 matic duct." 



None of these features are exclusive to the Plectognathi or diagnostic 

 of the group. The scales would not remove the representatives from 

 the Acanthopterygious fishes; the vertebrae of Psilocephalus {Anacan- 

 fhus Gthr.) and ClionerMnus {Xenopterus Gthr.) are more numerous than 

 in a large proportion of the Acanthopterygians ; the pectinate gills are 

 shared with fishes generally; a "narrow gill opening" is found in fishes 

 belonging to the same families {e. g., Cottidaj and Blenniidce) as those 

 having wide gill openings ; the mouth can scarcely be said to be nar- 

 row when it is coequal with the width of the wide-headed species, and, 

 on the other hand, very many Acanthopterygious fishes have the mouth 

 narrow; the bones of the upper jaw are at least as firmly united in 

 various Acanthopterygians {e. g., Teuthididae, Siganidae, IsTemophididae, 

 &c.) and Malacopterygians {e.g., some Oharacinidre, Dalliidae, &c.), as in 

 the Plectognath Triacanthids and Balistids. The other characters are 

 still less exclusive and more general. 



Were such the only characters assignable to the " order Plectognathi," 

 the group could not be retained. Nevertheless, most of the characters 

 above given do really belong to the group in question, and they can be 

 supplemented by characters of much more importance than those re- 

 hearsed, and are embodied in the following diagnosis : 



* Gunther's " Introduction to the Study of Fishes," p. 683. 1880. 



