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PACIFIC SCIENCE, Vol. XIX, October 1965 
KEY TO THE SPECIES OF THE GENUS Gnathophausia* 
a. Antennal scale small, not jointed, no strong rib terminating in a spine on outer margin; outer 
margin serrate. Epimera of sixth abdominal segment united ventrally, forming together a 
cordiform, concave plate, incised at apex. Dorsal keel of carapace interrupted. Lower lateral 
keel not curving upward behind, but terminating in a spine at the postero-inferior angle. 
Branchiostegal lobe generally with a well developed spine (sometimes obsolete). Maxilli- 
peds with a small exopodite. 
b. Both lappets of the epimera of the second to fifth abdominal segments pointed and 
spiniform. Antennal scale subovate, apex shortly pointed ingens 
b'. Anterior lappet of the epimera of the first to the fifth abdominal segments small, 
rounded; posterior lappet pointed and spiniform. Antennal scale sublanceolate, taper- 
ing to a sharp spiniform point. ................. gigas 
a'. Antennal scale large, of usual form, jointed at the extremity, outer margin formed by a strong 
rib terminating in a spine. Epimera of sixth abdominal segment not confluent ventrally. 
b. Lower lateral keel of carapace not curving up behind, but terminating in a spine on the 
postero-inferior angle of the carapace. Median keel of carapace interrupted, with spini- 
form serrations. Median line of abdominal segments with strong spines. Upper lateral 
keel of carapace wanting. Two epimeral spines on each side of the anterior section of the 
sixth abdominal segment. Maxillipeds with exopodite. gracilis 
b'. Lower lateral keel of carapace curving up behind; no spine at postero-inferior angle of 
carapace. Median keel of carapace not interrupted, without spiniform serrations. Median 
line of abdominal segments— if armed at all — -only with posteriorly projecting, small 
spines. Upper lateral keel of carapace present, very rarely wanting. Maxillipeds without 
exopodite. 
c. Two epimeral spines on each side of anterior section of sixth abdominal segment. 
Upper lateral keel of carapace present. Antennal spine obsolete. Branchiostegal lobe 
with a well-marked triangular spine. Spine of outer margin of antennal scale project- 
ing considerably beyond terminal lobe, serrated on both margins. . . longispina 
c'. One epimeral spine on each side of anterior section of sixth abdominal segment. 
Antennal spine more or less distinct. Branchiostegal lobe without spine, generally 
rounded, rarely angular. Spine of outer margin of antennal scale not, or only 
slightly, projecting beyond terminal lobe. 
d. Upper lateral keel of carapace present. 
e. Abdominal segments dorsally slightly keeled, with small, posteriorly 
projecting spines. Epimera of five anterior abdominal segments pointed 
posteriorly. Branchiostegal lobe rounded. 
f. Carapace not suddenly constricted anteriorly and forming no 
shoulder. Branchiostegal lobes moderately developed. . . zoea 
{'. Carapace suddenly constricted anteriorly, forming a distinct shoul- 
der in front of the anterior ends of the upper lateral keels. Bran- 
chiostegal lobe greatly expanded. ...... scapularis 
( or zoea var. scapularis ) 
5 Based on Ortmann, 1906, with alterations. 
