316 CALIFORNIA ACADEMY OF SCIENCES. 



the tail, the line curving upward at base of the caudal 

 fin; a series of pores extends on either side of the lateral 

 line and its branches. 



Dorsal fin short, the spine slender, 2|--3 in head, its 

 insertion variable; adipose fin very small. 



Caudal deeply forked, the lobes pointed. 



Ventrals small, extending to the anal in the young, 

 shorter in the adult. 



Pectoral spine reaching to the anal, 2J in length of 

 head; shorter in the adult. 



Color brassy or silvery, darker above; fins sometimes 

 with a dark border. 



Head 3|-4J; depth 4J-5J; Br. 14; D. I, 6; A. 68. 



Nine specimens, .12-40 m. Para. Thayer Expedition. 



FAMILY V. PYGIDIIDJE. 



>Siluroidei trichomycteriformes Bleeker, Nederl. Tij- 

 dschr. Dierk. i, 112, 1863. 



^>8iluridce opisthopterce Giinther, Cat. Fish. Brit. Mus. 

 v, 4, 1864. 



>Siluridce branchicolce Giinther, 1. c. 



> Trichomycteridce Gill, Arrangement of Families of 

 Fishes, 19, 1872. 



=Pygidiidce E. & E. Am. Nat. July, '88. 



Air bladder rudimentary, enclosed in the lateral pro- 

 cesses of the coalesced vertebrae. Adipose fins none. Dor- 

 sal and anal short. Skull enveloped in a thick coat of 

 muscles and skin. Teeth usually villiform. Nares re- 

 mote. Derm naked. 



The members of this family vary greatly. Cetoi>i* 

 is the most aberrant of the genera, approaching most 

 closely some genera of Auchenipteriiue, with which it 

 has usually been associated. Its coalesced vertebrae 

 and air bladder are, however, essentially like those of 

 Pyyidium. Its dorsal fin while placed well forward is 



