with prominent undivided median carina on pos- 

 terior process ; carina exposed owing to slight di- 

 vergence of anteromedian corners of lateral plates. 



Description 



ROSTRUM (fig. 20 a, b) 



Teeth ^> mode- (percentage distribution: 



1-3 2 



8/2—67, 9/2—21, 8/3—5, 7/2—4, 9/3—2, 7/1—1; 

 N = 300)+ epigastric; position of ventral teeth 

 variable, first tootli situated from well anterior to 

 slightly posterior to distal dorsal tooth; rostrum 

 relatively short in larger juveniles, reaching at 

 most to base of lateral ant«nnular flagellum ; at- 

 taining maximum length in relation to carapace 



r.l. 

 length at 8 to 13 mm. c.l. (ratio — as high as 



c.l. 



0.75) ; decreasing progressively with increasing 



length of shrimp, rostriun reaching distal end of 



first antennular segment in shrimp 50 nun. c.l. 



(ratio — reduced to about 0.35) ; rostriun straight 

 c.l. 



apically or directed downward, occasionally up- 

 turned, convex proximally; highest portion of 

 blade at level of third dorsal tooth; latter level 

 with anterior margin of carapace ; rostrum tip l^ 

 to 1/4 r-1- Postrostral carina strong, prominent, 

 uniform in width or sliglitly wider in anterior 

 half, and long, extending almost to posterior 

 margin of carapace. Median sulcus deep tlirough- 

 out, long, ending near posterior margin of cara- 



FiGURE 20. — Pe^iaeus (M.) duorarum duorarum Burkenroad. a. Rostrum, 9 37 mm. c.l., off Sebastian, ila. 



b. Rostrum, S 35 mm. c.l., off Melbourne Beach, Fla. 



WESTERN ATLANTIC SHRIMPS OF GENUS PENAEUS 



503 



