FreruE 4. — Penaeus (L.) setiferus (L). Rostrum, 9 36 nim. c.l., off Cocoa Beach. Fla. 



internal margin, and with long setae along 

 proximal one-fourth of external margin; in fe- 

 males processes lacking but long setae present 

 along proximal two-fifths of external margin. 

 Those processes were described by Rioja (1939) 

 and Young (1959) ; the latter worker stated that 

 "Since the antennular flagella are olfactory, the 

 sexually dimorphic medial fiagellum of the male 

 Penaeus setiferus probably functions to enable the 

 male to find the sexually mature female during the 

 time of mating." Anterolateral spine small, sharp. 

 Stylocerite reaching slightly beyond midlength of 

 first antennular segment. Prosartema extending to 

 proximal fourth of second antennular segment. 



ANTENNAE 



ScajDhocerite length 2i/^ times maximum width ; 

 spine reacliing or slightly surpassing distal end of 

 third antennular segment. Carpocerite about II/4 

 times longer than wide, its distal end reaching base 

 of eye. Antenna! flagellum very long, 21/^ to 3 times 

 body length ( fig. 6) . 



THORACIC APPENDAGES 



Third maxilliped reaching at least distal end of 

 first, and at most distal end of proximal % of 

 second antennular segment ; length of dactyl % 

 to % of propodus. First pereopod extending 

 to distal end of carpocerite or surpassing it by as 

 much as four-fifths length of dactyl. Second pere- 

 opod reaching distal end of first and, at most, dis- 

 tal end of proximal tliree-quarters of second anten- 

 nular segment. Third pereopod extending to distal 

 end of antennular peduncle or surpassing it In; 



length of entire propodus. Fourth pereopod exceed- 

 ing carpocerite by % to % length of propodus. 

 Fifth pereopod surpassing fourth by one-half to 

 entire length of dactyl. Exopods on all pereopods; 

 long ischial and basial spines on first pereojiod, and 

 rather long basial spine on second pereopod. 



ABDOMEN 



Carinate dorsally from one-quarter of third or 

 from fourth somite jjosteriorly, carina gradually 

 increasing in lieight posteriorly forming keel on 

 sixth somite, and ending in sharp spine on posterior 

 margin of somite. Dorsolateral sulcus (fig. 7) very 

 shallow and narrow, without lips; in yomig in- 

 dividuals running almost entire length of somite, 

 in adults extending only from slightly anterior of 

 midlength of somite to near posterior margin. 

 Sixth abdominal somite with three cicatrices on 

 each side, anterior one longest; fifth somite with 

 one cicatrix and diagonal series of minute pits an- 

 terior to sinus on posterior margin of somite 

 situated on rib in large specimens; fourth somite 

 with similar series of pits dorsal to sinus on 

 posterior margin of somite. Ventral margin of 

 pleuron of first somite slightly to moderately in- 

 dented. Telson (fig. 8) with deep median sulcus 

 and acuminate tip. Dorsoventral axis of larger 

 males much shorter than that of females of cor- 

 responding lengths. 



PETASMA (fig. 9 a-c) 



Lateral lobe with distal portion of inner surface 

 bearing conspicuous rounded fold and diagonal 

 ridge, which undulates proximally to near mid- 



WESTERX ATLANTIC SHRIMPS OF GENUS PENAEUS 



