Basial spimes on first and second pereopods, exo- 

 pods on first four pereopods and usually on fiftli. 

 Petasma symmetrical, ijodlike, with or without 

 distomcdian projections, and with lateral lobes 

 usually armed with long ^-entral costae. Appendix 

 masculina subtriangidar to ovoid, bearing spines. 

 Thelycmn often with median protuberance at 

 posterior margin of sternite XIII, open or usually 

 with two lateral plates covering or almost covering 

 sternite XIV. Zygocardiac ossicle consisting of 

 principal tooth followed by longitudinal row of 

 smaller teeth often ending in cluster of minute 

 teeth. Pleurobranchiae on somites IX to XIV; 

 rudimentary arthrdbranch on VII, and posterior 



arthrobranch on XIII somites; mastigobranchiae 

 on VII to XII somites. Body glabrous (after Dall, 

 1957, modified) . Figures 1 to 3 illustrate characters 

 used in Penaeus taxonomy. 



Two divisions of the genus Penaeus were recog- 

 nized by Burkenroad (1934) : in Division 1 he 

 placed the species with a short adrostral carina 

 (not approaching the posterior margin of the cara- 

 pace) and lacking a gastrofrontal carina, and in 

 Division 2 the species with a long adrostral carina 

 (almost reaching the posterior margin of the 

 carapace) and possessing a gastrofrontal carina. 

 Kubo (1949) recognized Burkcnroad's Division 2, 

 although he used the adrostral sulcus instead of the 



rostral tooth 



antennal spine 



gastrofrontal sulcus 



gastrofrontal carina 



gastro orbital carina 



orbito antennal sulcus 



antennal carina 



hepatic spine 

 cervical sulcus 



epigastric t ooth 

 hepatic carina 

 median sulcus 



postrostral carina 

 adrostral sulcus 

 adrostral carina 



Figure 1. — Dorsal and lateral views of carapace showing features used in Penaeus taxonomy. 

 WESTERN ATLANTIC SHRIMPS OF GENUS PENAEUS 



463 



