14 BULLETIN 189, UNITED STATES NATIONAL MUSEUM 



hh. Pectoral fins confluent with the head and body, forming a more or less 



definite disk; nostrils situated on ventral side of snout. 

 i. Tail comparatively thick, usually bearing 2 dorsal fins and a caudal 

 fin; no serrated spine present. 

 j. Snout not produced; disk broad, subcircular or rhomboidal. 



k. Disk subtjircular; skin naked, soft and smooth; electric organs 



present Torpedinidae (p. 48) 



kk. Disk rhomboidal, skin usually more or less rough, with small spines 



and larger tubercles; no electric organs Bajidae (p. 52) 



jj. Snout not produced, tapering; disk more or less triangular. 



Bhinobatidae (p. 50) 

 it. Tail slender, usually without a dorsal fin, generally at least with a 

 large serrated spine. 

 I. Pectoral fins confluent around snout; eyes superior; teeth small, nu- 

 merous, usually with ridges or small cusps Dasyatidae (p. 63) 



II. Pectoral fins ending opposite sides of head, united or free from rostral 

 fins; eyes lateral; teeth large, few, flat, more or less hexagonal, mid- 

 dle ones usually much broader than outer ones. Aetobatidae (p. 74) 

 aa. Gill opening single, leading to 4 slits; teeth united, forming bony plates; body 

 compressed; tail slender; proboscis produced into a leaf-shaped flexible 



appendage Callorynchidae (p. 76) 



///. Pisces (true fishes): Body variously formed; skeleton bony; skull well devel- 

 oped; mouth well developed, with jaws attached to the skull; gill opening 

 single on each side; gills attached to bony arches; claspers wanting. 

 a. Eyes on opposite sides of head; both sides of fish pigmented. 

 b. Ventral fins present. 



c. Ventral fins abdominal (that is, attached somewhere to abdomen). 

 d. Adipose fin present. 



e. Body naked; dorsal and pectoral each with a strong spine; maxil- 

 lary with 1 and chin with 2 or more barbels. _ Ariidae (p. 119) 

 ee. Body covered with scales; fins without spines. 

 /. Body little if at all compressed, not provided with light organs 



(photophores) Synodontidae (p. 108) 



//. Body compressed, provided with conspicuous light organs, at least 

 on lower part of side. 



g. Margin of upper jaw formed by maxillaries and premaxil- 

 laries; light organs confined to lower part of side and of head. 



Maurolicidae (p. 105) 



gg. Margin of upper jaw formed entirely by narrow premaxil- 



laries; light organs not wholly confined to lower part of side 



and of head, often present on upper surface of head and of 



caudal peduncle Myctophidae (p. 116) 



dd. Adipose fin absent. 



h. Dorsal fin single, composed of soft rays only. 



i. Snout, both jaws, or lower jaw onlj% greatly produced; body long, 

 very slender. 

 j. Snout greatly produced, tubelike, with a small mouth at its tip. 



Fistularidae (p. 150) 

 jj. Snout not greatly produced, not in form of a tube. 



k. Both jaws very long, each with a band of pointed teeth. 



Belonidae (p. 143) 



kk. Upper jaw short, lower one very long; no teeth on produced 



part Hemiramphidae (p. 144) 



