1 cm. 



Figure 68. — Penaeus (M.) brasiliensis Lat. Rostrum, cf 38 mm. c.l., Arvoredo, Santa Catarina, Brazil. 



ANTENNAE 



Scaphocerite length 21/^ to 2% times maximum 

 width, its length, relative to carapace length, de- 

 creasing slightly with growth; spine reaching 

 distal end of antennular peduncle. Carpocerite 

 length 1% width. Antennal flagellum alx)ut 1% 

 t.l. of shrimp. 



THORACIC APPENDAGES 



Tliird maxilliped reaching at least one-half of 

 first, but not beyond distal half of second ajiten- 

 nular segment; length of dactyl % to % that of 

 propodus. First pereopod reaching at least three- 

 fifths length of carpocerite or exceeding it by 

 dact}']. Second pereopod surpassing carpocerite 

 by half lengtli of dactyl to one-tenth that of carpus. 

 Third pereopod reaching at least base of second 

 antennular segment and, at most, exceeding third 

 antennular segment by entire length of dactyl; 

 proportionately longer in juveniles. Fourth pere- 

 opod reaching at least base of carpocerite and at 

 niost surpassing it by length of dactyl. Fifth pere- 

 opod subequal to fourth. 

 ABDOMEN 



Carinate dorsally from posterior half of fourth 

 somite, posteriorly carina gradually increasing in 

 height to form keel on sixth somite, ending in 

 shai-p spine on posterior margin. Doi-solateral sul- 

 cus (fig. 70 a, b) with both lips sharp, variable in 

 width, broad in populations from South America, 

 ratio Ijetween height of keel and width of sulcus 

 (K/S) ranging 1 to 4.5, modally 2 (fig. 71), nar- 

 rower in specimens from the West Indies north- 

 ward, K/S ranging from 3 to 9, modally 5 (fig. 73) . 



In South America, K/S is also modally 2 in all 

 size classes except 16 to 22 mm. c.l. with K/S mod- 

 ally 2.75 (fig. 72) . In West Indies- Central America 

 region and northward, K/S mode varies in dif- 

 ferent size classes — 5 in the smallest class and at 

 23 to 29 mm. c.l. ; 3 in the cla.ss intennediate be- 

 tween these two, and 3 in the largest (fig. 7-1). It 

 does not seem that any significance could be at- 

 tached to such a variation that does not show a 

 trend. Sixth abdominal somite with three cica- 

 trices on each side, posterior the smallest ; fifth ab- 

 dominal somite with one cicatrix and series of 

 minute pits anterior to sinus on posterior margin 

 of somite; fourth abdominal somite with similar 

 series of pits dorsal to sinus on posterior margin 

 of somite. Telson unarmed, with deep median sul- 

 cus and sharj) pointed tip. 

 PETASMA (fig. 75 a-c) 



Ventral costa broadening and curving gradually 

 from apex to distal end of ventromedian flap, ex- 

 tending almost straight proximally; distal ix)r- 

 tion unaiTned along free border and with 6 to 12 

 pointed teeth set in two irregular rows on attached 

 border; apex free from distal margin of ventro- 

 lateral lobide. Distal fold intruding considerably 

 inside petasma, forming large, rounded auricle 

 with numerous proniinent spines arranged dis- 

 tally in half moon on inner surface. Ventrolateral 

 lobule with external armature consisting of single 

 or pair of series abreast distally, increasing in 

 number proximally. Distomedian projections long, 

 fingerlike in appearance, extending well over dis- 

 tal portion of ventral costae. 



WESTERN ATLANTIC SHRIMPS OF GENUS PENAEUS 



567 



