HAMMERHEAD SHARKS — GILBERT 45

limits of itsrangein the easternAtlantic areuncertain, although it

has never

been

recorded

from

theBritishIsles.

Sphyrna

lewini is

found

in the western Pacific

from

southern Australia north to southern

Japan and

Korea,

and

in the eastern Pacific

from

northwestern

South America

to the Gulfof California.

The

factthatit isthe onlyspecies of

hammerhead

definitelyrecorded

from

the

Hawaiian

Islands (Gosline

and

Brock, 1960, p. 91)

may

indicate that it is a

more

pelagic species than

Sphyrna

mokarran,

which

alsologically

might be

expectedtooccurthere.

r I

mS\ mii^-iriAxAiyjzj

Map

^3.

—

Distribution ofSphyrnalewini.

(Themostwesterly recordfromAfricaisnowknowntorepresent S. couardi; solid⁼ mens examined; hollo

w=

confirmed literature references.)

:speci-

Sphyrna

lewini apparently does not extensively penetrate cool waters (i.e., in

which

the temperature does not rise

above

the

low

70'sF.).

Although

itsrange overlaps thatof S.zygaenato

some

extent, there are relatively

few

recordsofthe

two

species

having been

taken together (Herald, 1961,p. 31,fig.).

Sphyrna(Sphyrna) couardiCadenat Plates9a, 10a

SphyrnacouardiCadenat,1951, pp. 98-99. (Original description;comparedwith S. diplana and S. bigelowi; tipsof pectoral fins described as wliite; type locality: "offWestAfrica".)

Specimens

examined.

—

-Guinea:

USNM

uncataloged (1 head,

425 mm.

inwidth),12°06'

N,

17°22'

W.

Discussion — Sphyrna

couardi

was

described

by Cadenat

(1951, pp.98-99)

from

"off

West

Africa."

The

description

was

very brief

and

there

was no

illustration,although the

form was

said toresemble S.diplana(

=

S. lewini), differing

from

thatspecies(and

from

all other

members

ofthefamilySphyrnidae) in

having

theinferiorpartofthe pectoralfin white

and

alonger

and

smallerhead.

WhUe

I

have not

seen a

whole specimen

of S. couardi, I

have examined

a large

head

(USNM

uncatalogued) collected

by

Dr.

Bruce

B.

CoUette from

off

West

Africa. This head,

which

is

425 mm.

wide, has

been compared

with the

head

ofa typical

specimen

ofS. lewini,

445 mm. wide (USNM

46 PROCEEDINGS OF THE NATIONAL MUSEUM

^{vol. no}

uncataloged),

from

the

same

geographic^area.

Photographs

ofthese appearin plate 10

and

radiographsinplate9.

The most

striking difference

between

the

two heads

is the deeper,

more

robust

appearance

ofS.couardi (also see

measurements

intable 10). Thisisconfusing, since

Cadenat

describedS.couardias

having

a

"longer

and

smaller"

head than

S. lewini; however, this apparent discrepancy

may

simply

be

a

matter

of semantics.

The

overall

appearance

of the head,infact,

seems

closerto S.

mokarran

thanS.

lewini;however, couardi

and mokarran may readUy be

distinguished

by

the presenceofadistinct intranarialgroove

and

nonserratedteeth inthe former^species,

and by

chondrocranialstructure

and

differences inpore patterns

on

the ventralsurface ofthehead.

The mucal

pore patches

on

the ventral surface of the

head

are basicaDy similar in S. couardi

and

S. lewini, although the anterior-

median

patchinthe formeriscompletely separated medially instead of being divided

about halfway

as in the latter (fig. 22d).

The

chondrocraniaof the

two

formsalso are similar (pis.9a, b),the

main

difference being in the

appearance

of the preorbital process. In (S.

couardi thisstructureisshorter

and

has adistinct

knob

atthe angle,

whereas

inS. lewiniit islonger

and

lacksadistinctknob. Inaddition, theolfactory

wings

in S.couardiareblunt

and do

not

come

toasharp pointas in S. lewini. Inthiscase, however, the

wing

tips arerather raggedinappearance, suggesting thatthispossibly

may be an

aberrant condition.

In conclusion, the

above

evidence

seems

to indicatethat

Sphyrna

couardiisavalid speciesofrestrictedrange

and

thatit is

most

closely related to

Sphyrna

lewini.

Subgenus Platysqualus Swainson

The subgenus

Platysqualus,

which

is here considered to include

Sphyrna

tudes,S.media, S. corona,

and

S.tiburo, isdistinguished

by

thefollowing

unique

characters: First

and

fifthgillslitsnearly equal inlength

and both somewhat

shorter than thethree

middle

slits;anal fin

and

analfinbase longer thanin

any

other

group

ofsphyrnids, the former 11.0 to 13.5 percent,

and

the latter 7.5 to 9.0 percent, of

TL;

anal base a fourth ^{to half} again aslong as pectoralbase;

upper

pre- caudalpitbroadlysemicircular or slightlypointedinshape, the ends pointing anteriorly ^{(figs.21e-'i);} lower precaudai pit present (this featm-e also

sometimes

presentin S. lewini); fifth gill slit

above

in- sertion of pectoral fin (slightly posterior in S. tiburo); lobe of first dorsalfin extending pastinsertion of pelvic fin (in all

but

S. tiburo)

;

teethweak, nonserrated, with

narrow

pointedcusps; accessoryrostral cartilages oftenpresent (none observedin S.tiburo).

NO. 3539

HAMMERHEAD SHARKS GILBERT 47

Inaddition, the

subgenus

ischaracterizedby:

A

fairlyhigh second dorsalfin, itsgreatestheight about equalto greatestheightofanalfin

;

a shallowlyfalcate analfin; e^^es situated anterior to

mouth,

a line

drawn between

the posterior

margins

of orbitspassinganterior to

sym-

physisofjaws (intersecting

symphysis

inlargerspecimensof S.tiburo);

asmallorbit,separated

from

nares

by

adistancegreaterthan horizon- taldiameterof orbit;absenceofan outernarialgroove;a variable total

number

of vertebrae, rangingin

number from

142 to 202,

mth

those overposteriorpartofcoelomic cavity not enlarged;asmall

maximum

size,probably not exceeding4 or 5feet.

Perhaps

the

maximum

size in

some

casesis

even

less (e.q., S. corona).

Sphyrna(Platysqualus) tiburo (Linnaeus)

Diagnosis.

—

-Characters

mentioned

inthediagnosis ofthe

subgenus

Platysqualusarenot repeatedhere.

Sphyrna

tiburois

unique among members

of thegenus

Sphyrna

in havingthe

head

onlyslightlyexpanded,eitherspadeorshovelshaped,

and measuring from

14.4 to24.5percent of

TL

in specimens

up

to 1,000

mm.

long (higher values usually apply to smaller individuals and/or to individuals of the subspecies vespertina).

The

anterior-

median

pore patch

on

the underside of the

head

is also unique, the patch characterized

by

arathersharp,

but smoothly rounded

angleat the posteriorcorner

and by

a long,

narrow median

posteriorextension

(fig.226).

Sphyrna

tiburois alsodistinguished

by

the anterior

margin

of the

head

being

more

orlessevenly

rounded between

theej^es,with neither a

median

scallopnornarialdepressionspresent;

no

innernarialgroove;

origin offirstdorsalfindistinctlyposterior toaxilofpectoralfin,a per- pendicularline

drawn

ventrally

from

origin ofdorsal intersectingpos- teriorpartof pectoralfin;teethnotserrated,withshort,weak, rather bluntcusps.

A comparison

of

Sphyrna

tiburowith other

members

ofthe genusis

presented intable 1.

Description.—

Meristicdata appearⁱⁿ table6. Characters

men-

tioned in thediagnosesofthe

subgenus

Platysqualus

and

of S. tiburo arenot repeatedhere.

Intranarial distance

from

one-tenth to one-sixth of

TL

(lower values usually apply to larger individuals); outer posterior corners oflateralexpansions oflieadbroadly

rounded and

situated posterior to corners of

mouth;

narial flap broad, blunt at tip, with the outer edge curving gradually inward; length of snout

about

two-fifths of

head

width;greatest transversedistance

between

cornersof

mouth from

one-third to a little

more

than two-fifths of greatest

width

of head; sjTnphysis of jawssituated, in smaller individuals, slightly

48 PROCEEDINGS OF THE NATIONAL MUSEUM

^{vol. 119}

anterior to a transverse line

drawn between

posterior

margins

of orbits, while inlargerindividuals aline

drawn between

thesepoints passes through the symphysis;a

weakly marked

^labialfurrow present

on

lower

jaw

only, the furrow extending only a short distance (con- cealed

when mouth

isclosed)

.

Fourth

gill slitsituated anterior to,

and

fifth gill slitslightly pos- terior to, insertion of pectoralfin; posterior lobe of first dorsal fin terminating just anterior to insertion of pelvic fin (the dorsal

and

pelvic finsbeing incloserproximity onlyin S. tudes, S. corona,

and

S. media); first dorsal fin relatively slender, not perfectly erect, a line

drawn

perpendicularly

from apex

offin barelyintersectinglobe offin;base offirst dorsalfin

about

two-fifthslength of

head and

at least half again length of pectoralfin base; anterior

margin

of first dorsalfinevenly curved, with the part nearest theapex

more

strongly curved; distal

margin

of first dorsal fin

moderately

falcate; lobe of first dorsal fin

from

four-ninths to almost one-half length of first dorsalbase;origin of seconddorsalfinsituated

about

athird of

way back above

baseofanalfin;seconddorsalfinrathertall, itsgreatest height

about

two-thirds length ofbase,

and about

equal togreatest height of anal fin; second dorsal fin base about five-eighths of anal finbase;lobeofseconddorsalfinratherlong,itslength

about

a third again greatest height of

same

^fin,

and

extending

about

two-thirds of distance

from

posteriorpart of second dorsalbase to

upper

pre- caudal pit; anterior

margin

of pectoral fin

from

one-half to nearly two-thirds length of

head

(higher values usually apply to larger individuals); pectoral fin four-fifths as

broad

as long; pectoral fin base five-eighths to three-fourths length of anal fin base; anterior

margin

of pectoral

moderately

convex; distal

margin

of pectoral nearly straight;

apex and

inner corner of pectoral

rounded;

pelvic fin

about

three-fourthslengthofanalfin;pelvicfinbase

about

three- fourths length of anal fin base; anterior

margin

of pelvicfin

weakly

convex; distal

margin

of pelvic fin very shallowly falcate; anal fin

about

one-fourth again as longas pelvicfin; analfinbase

from

one- fourth to over one-third again as long as pectoral

and

pelvic fin bases,

and from

three-fifths again to nearly twice as long as second dorsal fin base; height of anal fin

about

equal to greatestheight of second dorsal fin; anal fin

weakly

falcate

toward apex and

nearly straight

toward

tip of lobe; caudal fin

from

one-fourth to nearly one-thirdof total

body

length;

upper margin

ofcaudal nearly^straight;

terminal partofcaudal

about

one-fourthof totallengthoffin;posterior

margin

of terminal part of caudal fin nearly straight or shghtly falcate;

both

terminal

and

lower apices of caudal

narrowly rounded

in smaller specimens,

somewhat more

pointed inlarger individuals;

lowercaudal lobe appearingrelatively

broad and

short, the distance

NO. 3539

HAMMERHEAD SHARKS — ^GILBERT 49