Two nostrils on each side; basis cranii simple; gill-opening narrow, above base of pectoral .......... 4. Rhamphocottidae.
B. Ventral fins, if present, not widely separated; one or several of the pterygials in contact with the clavicle.
Ventral fins distinct; gill-clefts wide .......... 5. Cottidae.
Ventral fins united into a sucking disk; gill-opening narrow, above base of pectoral .......... 6. Cyclopteridae.
C. Ventral fins widely separated; none of the pterygials in contact with the clavicle.
Ventral fins behind base of pectorals; praecaudal vertebrae without transverse processes .......... 7. Platycephalidae.
Ventral fins a little in front of base of pectorals; praecaudal vertebrae with transverse processes .......... 8. Hoplichthyidae.
II. Head completely cuirassed.
Ventral fins narrowly separated; no pectoral appendages; pterygials short and broad .......... 9. Agonidae.
Ventral fins widely separated; 2 or 3 lowermost rays of pectoral fin detached as feelers; pterygials short and broad .......... 10. Triglidae.