2. No scales. Uody more or less encased in derinal 

 bony plates. Lateral line canals absent. 



a. Two dorsal fins. Ventrals abdominal, rudi- 

 mentary. Tail ventrally deflected, naked, 

 moveable. Trunk encased in cuirass of bony 

 plates. Four branchiostegals. Gillopenings of 



moderate width. Gills pectinate • . . CentrisciJac p. i8. 



b. Two dorsal fins. Ventrals abdominal, large, 

 with I spine and 6 rays. Skin with a longi- 

 tudinal and transverse series of large stellate 

 ossifications, rendering anterior part of trunk 

 immoveable. One branchiostegal. Gillopenings 



wide. Gills lobate Soknostomidae p. 24. 



c. One dorsal fin or none. No ventrals. Pectorals 

 may be wanting. A complete cuirass of dermal 

 'bony plates forming rings round the body. 

 One to three branchiostegals. Gillopenings 



reduced to small dorsal apertures. Gills lobate. Sy/ig/iaihidac jj. 30. 



I. Fam. AULOSTOMATIDAE. 



Physoclists. Body elongate, covered with scales or with 

 minute spinelets or naked, in which case there may be bony 

 plates in various parts of the body, mostly covered by skin. 

 Lateral line continuous. Tail short. Snout long, tubiform. Mouth 

 terminal, not protractile, bordered by the small intermaxillaries, 

 which are edentulous or provided with teeth, behind them the 

 rather large maxillaries. Mandibles and vomer with minute teeth 

 as also the palatines or pterygoids. Two nasal openings. Supra- 

 occipital small, wedged in between the posterior part of frontals 

 and excluded from occipital foramen; parietals wanting; post- 

 temporal present, from it is suspended the cleithrum, with or 

 without a supracleithrum (supraclavicular); postcleithrum (post- 

 clavicle) present. The 4 anterior vertebrae much elongate and 

 suturally united into one piece; their transverse processes 

 form a continuous lateral, .their spinous processes a continuous 

 vertical lamella. To it are fastened three median, long, bony 

 nuchal shields covered by skin and to be regarded as modi- 

 fied interspinous (interneural) bones. Opercular apparatus well 

 developed. Four or five branchiostegals. Gillmembranes separate, 

 free from isthmus. Four complete, pectinate gills; gillrakers 



