34 
BULLETIN OF THE BUREAU OF FISHERIES 
III. ELASMOBRANCHII (Sharks, skates, and rays). — Skeleton cartilaginous; skull imperfectly 
developed; brain present; gill openings slitlike, five to seven on each side; skin with small, 
rough scales, spines, or tubercles, or naked; air bladder absent; jaws separable from the skull. 
1. Body elongate, usually more or less rounded, not greatly depressed and not forming a disk; 
gill openings all or partly lateral; pectoral fins not attached to the head. 
Euselachii (the typical sharks). 
a. Body typically fishlike; one or two dorsal fins present; anal fin present. 
b. Head normally shaped, not broad and expanded across the eyes. 
c. Nictitating membrane absent; each nostril with a cirrus or barbel; two or three gill 
slits over base of pectoral Orectolobidx (nurse sharks), p. 44 
cc. Nictitating membrane absent; nostrils without a cirrus or barbel; gill slits all in 
advance of pectorals; mouth broad, mainly transverse 
Lamnidx (man-eater sharks), p. 45 
ccc. Nictitating membrane present, nostrils without a cirrus or barbel; last gill slit above 
base of pectoral; mouth narrow, crescent-shaped Galeidx (gray sharks), p. 46 
bb. Head greatly expanded across the orbital region, more or less hammer-shaped 
Sphyrinidx (hammerhead sharks), p. 49 
Tectospondyli (the dogfishes and angel sharks). 
[ aa. Body more or less depressed; two dorsal fins present; anal fin absent. 
d. Head and body not greatly depressed; each dorsal fin preceded by a spine; pectoral 
fins not greatly expanded Squalidx (dogfishes), p. 51 
dd. Head and body notably depressed and expanded; dorsal fins without spines; pec- 
toral fins large, greatly expanded Squatinidx (angel sharks), p. 54 
[' 2. Head and body much depressed; gill openings all inferior; pectoral fins greatly expanded, 
attached to the head; anal fin absent. 
Batoidei (skates and rays). 
a. Tail comparatively thick, bearing two dorsal fins and no caudal spine. 
b. Body elongate, depressed, but not forming a disk; snout produced into a long, thin, saw- 
like process, armed on each side with a series of large, strong teeth 
Pristidx (sawfishes), p. 55 
bb. Body broad, forming with the pectorals a rhomboidal or subcircular disk; snout more or 
less produced, not sawlike, and never armed with teeth, 
c. Disk rhomboidal; skin usually rough, bearing spines, prickles, or tubercles; no electric 
organs present Rajidx (skates), p. 56 
cc. Disk subcircular; skin smooth, unarmed; an electric organ on each side of median line 
on head Torpedinidx (electric rays), p. 61 
aa. Tail usually very slender; bearing one or no dorsal fins and usually one or more strong, 
serrated spines. 
d. Disk subcircular or rhomboidal; pectoral fins uninterrupted confluent around the snout 
Dasyatidx (sting rays), p. 63 
dd. Disk broad and angular; pectoral fins not confluent around the snout; head bearing 
one or a pair of rostral processes or cephalic fins. 
e. Head bearing one or a pair of rostral processes; teeth large, flat, largel.y hexagonal. 
/. Snout with a pair of rostral fins, joined together and forming a single rostral 
process Myliobatidx (eagle rays), p. 68 
ff. Snout with two separate lobes, making the anterior margin of the snout concave 
Rhinopteridx (cow-nosed rays), p. 70 
ee. Head with a pair of cephalic fins, developed as two hornlike appendages; teeth 
small, numerous, in pavement Mobulidx (sea devils), p. 71 
IV. PISCES (The true fishes). — Skeleton usually bony, sometimes cartilaginous; skull with a well- 
developed system of bones; a single gill opening on each side; skin commonly with normally 
developed scales, sometimes with variously shaped bony plates and occasionally naked. 
1. Ganoidei (ganoid fishes) : Tail strongly heterocercal; arterial bulb muscular, with numerous 
valves. 
