114 Bulletin 4J, United States National Museum. 



OSTARIOPHYSI. 



This group, which iuclndes the great majority of the living fresh-water 

 fishes of the workl, is characterized chietiy by the nioditication of the 

 anterior vertebne. These are coossified and have some of their lateral 

 and superior elements detached and modified to form a chain of small 

 bones, the Weberian ossicles, which connect the air bladder with the ear. 

 The three orders, Nematognathi, Plectospondyli, and Scyphophoki 

 (Mormyrida), which compose this group, are doubtless derived from a 

 common stock, (oampioi', a little bone ; ^iaof, bladder.) 



Order M. NEMATOGNATHI. 



(The Catfishes.) 



Parietals and supraoccipital confluent. Four anterior vertebr* coossi- 

 fied, and with ossicula auditus or weberian apparatus. No mesoptery- 

 gium. Basis cranii and pterotic bone simple ; no coronoid bone. Third 

 superior pharyngeal bone wanting, or small and resting on the fourth ; 

 second directed backwards. One or 2 pairs of basal branchihyals ; 2 pairs 

 of branchihyals. Suboperculum wanting, or modified into the uppermost 

 branchiostegal. Mesocoracoid present. Premaxillary forming border of 

 mouth above, except in one family, Diplomystid.e, in which the maxil- 

 laries also bear teeth. Interclavicles present. No scales. Skin naked or 

 with bony plates. 



"This division isthe nearest ally to the sturgeons (Chondkostei) among 

 Physostomous fishes, and I imagine that future discoveries will prove 

 that it has been derived from that division hy descent. In the same way 

 the Isospondylous fishes are nearest the Halecomokphi, and have prob- 

 ably descended from some Crossopterygian, near the Haplistia, through 

 that order. The affinity of the catfishes to the sturgeons is seen in the 

 absence of symplectic, the rudimental maxillary bone, and, as observed by 

 Parker, in the interclavicles. There is a superficial resemblance in the 

 dermal bones." — (Cope, I. c, 454.) 



This group comprises the Silukid/E* and their relatives, now divided 

 into several families by Prof. Gill. (Silurid.e, Giinther, Cat., y, 1-277.) 

 (vi/iin, thread ; yvd-dnf, jaw ; from the maxillary barbels, which are always 

 present.) 



Analysis of Families of Nematognathi. 



a. Air bladder well develojied. usually simiile or with transverse coiistrictiuus, lying freo iu 

 the abdominal cavity. Mouth terminal; teeth villiforni, lunital, incisor or molar 

 like; intestines short; arranged iu longitudinal folds; body naked, or with one series 

 of lateral plates; diaphragm membranous; tip of scapular process reaching baei- 

 occipital. Dorsal fin short, coutiued to the abdominal part of the vertebral column; 

 opercle well developed and movable; adii)08e fin normally present; gill openings gen- 

 erally wide; caudal vertebra" not compressed, the neural spines simple, spine-like. 

 Maxillary rudimentary, forming the base of a long barbel, the premaxillaries alone 

 forming the margin of the upper jaw. Silueids:, xxxiv. 



* In the arrangement of the tropical genera of Nematognathi, wc liave followed closely the 

 "Revision of the South American Nematornatiii," by Eigenmann & Eigeumaun, 1890, 



