of propodus. Second pereopod surpassing carpo- 

 cerite by one-half of length of dactyl to entire pro- 

 podus. Third pereopod extending to distal end of 

 second or at most surpassing third ant«imular 

 segment by entire dactyl. Foiu'th isereopod reach- 

 ing base of carpocerite or exceeding it by entire 

 length of dactyl. Length of fifth pereopod sub- 

 etjual to that of fourth. Exojxyds on all pereopods; 

 long ischial and basial spines on first pereopod; 

 raf her long basial spine on second pereopod. 

 ABDOMEN 



Carinate dorsally from posterior half of fourth 

 somite, posteriorly carina gradually increasing in 

 height to fonn keel on sixth somite, ending in 

 sharp spine on posterior margin. Doi-solateral sul- 

 cus (fig. 22) very nai'row, ratio between height of 

 keel and ^yidtll of sulcus (at about one-third length 

 from posterior margin of somite) vaiying from 

 about 2.5 to 15.5 (modally 4.5, fig. 23) ; in some 

 specimens sulcus almost entirely closed. No signifi- 

 cant difference in K/S (ratio of the height of the 

 keel to the width of the sulcus) between males and 

 females at any size. Figure 24 shows K/S also has a 

 modal value of 4.5 in size classes to 22 mm. c.l. and 

 in the largest class, whereas K/S mode increases 

 slightly in intermediate classes. Lips sharp, bordei-- 

 ing sulcus to near posterior end, there sidcus widens 

 slightly in nearly oval depression. Sixth abdommal 

 somite with three prominent cicatrices on each 

 side, anterior one longest; fifth 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 unanned, with 

 deep median sulcus and shaq> ix>inted tij). 



Figure 22. — Penaeus (If.) duorarum duorarum Burken- 

 road. Sixth abdominal somite, po-sterodors-al iwrtion. 9 

 42.5 mm. c.l., off Long Key, Florida Keys. 



40 



30- 



20 — 



10 — 



2.5 



4.5 



6.5 



8.5 



10.5 



12.5 



14.5 



Figure 2.3. — Percentage of distribution of keel-.sulcu.s 

 (K/S) values in Penaeus (M.) duorarum duorarum 

 Burkenroad. 



PETASMA (fig. 25 a-d) 



Ventral costa broadening and turning prox- 

 imally rather abniptly, with ajjex adnate to mem- 

 branous side of ventrolateral lobule, distal jwrtion 

 armed along free margin with a series of 1 to 12, 

 usually 4 to 7, minute spines clearly distinct (even 

 in rather small juveniles 9 mm. c.l., about 42 mm. 

 t.l.), and on attached margin with compact 

 group of 6 to 16 prominent, often curved teeth. 

 Ventrolateral lobule with narrow band of minute 

 spines consisting of single series distally, pair of 

 series proximally followed by three or four longer, 

 closely set series. Distal fold of free margin of 

 lateral lobe small, intiiiding little inside petasma, 

 unarmed or with few spinules near free edge. 

 Distomedian projections rather thick and rela- 

 tively short, forming hood overhanging distal 

 portion of ventral costae. 



WESTERN ATLANTIC SHRLMPS OF GENUS PENAEUS 



505 



