end of adrostral sulcus, shallow, and often inter- 

 rupted. Dorsolateral sulcus usually narrow. Pe- 

 tasma with distal portion of ventral costa increas- 

 ing gradually in width proximally and turning in 

 arc; unarmed along free border and with elon- 

 gated group of closely set small teeth on attached 

 border ; apex of costa adnate to membranous por- 

 tion of ventrolateral lobule; latter rather exten- 

 sively covered with spines; distal fold small, usu- 

 ally with numerous si^inules, but sometimes un- 



) armed. Thelycum with anterior process relatively 

 broad, and with anteriorly bifurcate median ca- 

 rina on posterior process; lateral plates with an- 



I teromedian angles widely divergent, leaving me- 

 dian carina exposed. 



ROSTRUM 



r„ n 6-10 



Teeth 



Description 



mode - (percentage distribution: 



1-2 



8/2—57, 9/2—27, 7/2—7, 10/2—5, 8/1—1, 9/1—1, 

 7/1 — 1, 6/1 — 1, N = 200)+ epigastric; position 

 of ventral teeth variable, first tooth situated from 

 well anterior to slightly posterior to last dorsal 

 tooth; rostrum long, in larger juveniles and sub- 

 adults reaching to base of distal one-third of 

 thickened portion of lateral antennular flagellum, 

 attaining maximuni length in relation to carapace 



r.l. 



length at 18 to 23 mm. c.l. (ratio — — as high as 



c.l. 



0.85) ; decreasing progressively with increashig 



length of shrimp, rostrum reaching midlength 



of second antennular segment in shrimp 50 mm. 



r.l. 

 c.l. (ratio — — reduced to about 0.50); rostrum 

 c.l. 



usually strongly sinuous, proximal half convex, 

 distal half with dorsal margin strongly concave; 

 highest portion of blade at level of second or 

 third dorsal tooth; latter level with anterior 

 margin of carapace ; rostrum tij) 14 to almost 1/3 r.l. 

 Postrostral carina strong, usually exj^anded in 

 anterior half, and usually short, ending well 

 anterior to posterior margin of carapace. Median 

 sulcus shallow, usually interrupted, short, ending 

 well anterior to posterior margin of carapace. 

 Adrostral sulcus typically narrow jjosteriorly, 

 }i to % width of postrostral carina, tapering to 

 point posteriorly or turning laterally and broaden- 

 ing slightly at end; sulcus usually short, ending 

 % to i/i4 e.l. from posterior margin of carapace. 



occasionally ending 1/15 to y^g c.l. from carapace 

 margin. Adrostral carina prominent anteriorly, 

 sharp on carapace, same length as adrostral sulcus. 



CARAPACE (flg. 51 a, b) 



Length in proportion to total length smaller in 

 juveniles, increasing slightly at about subadult 

 stage. Gastrofrontal sulcus broad, extending to 

 about one-fifth c.l. Gastrofrontal carina sharp, 

 turning slightly posterodorsally, ending in acute 

 orbital angle anteriorly. Orbito-antennal sulcus 

 wide anteriorly, narrowing posteriorly to below 

 apex of hepatic spine, tliere widening again into 

 base of spine. Gastro-orbital carina very pro- 

 nounced, occupying approximately posterior four- 

 fifths of distance between postorbital margin and 

 hepatic spine. Antennal carina very prominent. 

 Cer^acal sulcus deep along entire length, 1/5 to 1/4 

 c.l., ending slightly anterior to midlength of cara- 

 pace. Hepatic carina 14 to 1/4 c.l., shaq), sloping 

 anteroventrally to end 1^2 to Vis c.l. from an- 

 terior margin of carapace. Antennal spine very 

 prominent; hepatic spine pronounced and acute. 



ANTENNULES 



Lateral flagellum relatively long, two-thirds 

 length of antennular peduncle, slightly longer 

 than median flagellum and witli articles sihorter 

 than those of median flagelkun. Anterolateral 

 spine small, sharp ; .stylocerite acuminate, reaching 

 slightly beyond midlength of first antennular 

 segment. Prosartema reaching distal end of proxi- 

 mal one-fifth of second antennular segment. 



ANTENNAE 



Length of scaphocerite 2I/2 times maximum 

 width; its length relative to carapace length de- 

 creasing slightly witli growth; spine reaching 

 basal tliickened portion of antennular flagellum. 

 Carpocerite about I14 times longer than wide. An- 

 tennal flagellum relatively short, li/o times total 

 length. 



THORACIC APPENDAGES 



Third maxilliped reaching at least end of first 

 antennular segment and at most two-thirds length 

 of second antennular segment; length of dactyl 

 three-fifths that of propodus. First pereopod 

 reaching only to midlength of carpocerite and at 

 most exceeding it by entire length of dactyl. 

 Second pereopod exceeding carpocerite by at least 

 length of dactyl and at most by one-quarter length 



WESTERN ATLANTIC SHRIMPS OF GENUS PENAEV8 



547 



