F. Carmona. 3 9 , INIBP-USNM, off Ciudad del 

 Carmen, April 29, 1959, R. Ramirez and M. 

 Flores. 2 cf 4 9, INIBP-USNM, NW. of Ciudad 

 del Carmen, 16 to 20 fm., April 29, 1959, R. 

 Ramirez and M. Flores. 1 (f, MCZ, NW. of 

 Arrecife Alacrdn, 6.5 km. of Whale Rock, 35 fm., 

 Blake Sta. 37. 



Diagnosis 



Adrostral sulcus broad posteriorly, and long, 

 reaching near posterior margin of carapace. 

 Median sulcus long, ending immediately anterior 

 to posterior end of adrostral sulcus, and deep along 

 its entire length. Dorsolateral sulcus broad. 

 Petasma witli distal portion of ventral costa in- 

 creasing gradually in width and turning proxi- 

 mally in arc, unarmed along free border and with 

 elongated group of closely set, small teeth on at- 

 tached border ; apex of costa adnate to membranous 

 portion of ventrolateral lobule, latter bearing ex- 

 tensive armature of closely set spines ; distal fold 

 small, usually with numerous spinules but some- 

 times unarmed. Thelycum with anterior process 

 relatively broad and with anteriorly bifurcate 

 median carina on posterior process ; carina ex^josed 

 owing to wide divergence of anteromedian angles 

 of lateral plates. 



Description 



ROSTRUM (fig. 39 a, b) 



5-10 8 ., . 



Teeth , mode -^ (percentage distribution: 



8/2—47, 9/2—44, 10/2—5, 9/3—1, 7/2—1.50, 

 6/2—0.50, 6/0—0.50, 5/2—0.50; N = 200) -1- epi- 

 gastric; position of ventral teeth variable, first 

 tooth situated from well anterior to slightly 

 posterior to last dorsal tooth; rostrum long, in 

 juveniles and subadults reaching as far as base of 

 distal 1/3 of thickened portion of lateral anten- 

 nular flagellum, attaining maximum length in 

 relation to carapace length at 13 to 20 mm. c.l. 



r.l. 

 (ratio — T- as high as 0.80) ; decreasing progres- 

 sively with increasing length of shrimp, rostrum 

 reaching at least three-quarters of second anten- 



nular segment in shrimp 50 mm. c.l. (ratio — - 



reduced to about 0.50) ; rostrum slender, sinuous, 

 with apical portion usually upturned, postero- 

 ventral margin concave; highest portion of blade 

 at level of second or third dorsal tooth; latter level 



with anterior margin of carapace; tip of rostrum 

 narrow, long, 14 to 1/3 r.l. Postrostral carina strong, 

 prominent, uniform in width or slightly wider in 

 anterior half, and long, extending to posterior mar- 

 gin of carapace. Median sulcus deep throughout, 

 often slightly wider in anterior half, and long, end- 

 ing near posterior margin of carapace. Adrostral 

 sulcus broad posteriorly, four-fifths to twice width 

 of postrostral carina, usually long, ending y^ to 

 i/^o c-1. from posterior margin of carapace. Adros- 

 tral carina prominent, sharp on carapace, long, 

 same length as adrostral sulcus, and parallel to 

 postrostral carina or inclined obliquely mesially at 

 posterior end. 



CARAPACE (fig. 40) 



Length in proportion to total length apparently 

 changing little, if at all, after juvenile stage is 

 reached (fig. -40). Gastro frontal sulcus broad, ex- 

 tending to about one-sixth c.l. Gastrof rontal carina 

 shaii5, turning slightly toward doreal margin 

 posteriorly, ending anteriorly in acute orbital 

 angle. Orbito-antemial sulcus wide anteriorly, nar- 

 rowing posteriorly to below hepatic spine, there 

 widening again into base of spine. Gastro-orbital 

 carina sharp, occupying approximately posterior 

 four-fifths of distance between postorbital margin 

 and hepatic spine. Antennal carina very promi- 

 nent. Cervical sulcus Vg to 14 c.l., ending slightly 

 anterior to middle of carapace. Hepatic carina % 

 to 14 c.l., sharp, sloping slightly anteroventrally to 

 end i/ig to 1/23 c-1. from anterior margin of carapace. 

 Antennal spine veiy prominent and acute ; hepatic 

 spine strong. 

 ANTENNULES 



Lateral flagelhun about two-thirds length of 

 antennular peduncle, slightly longer than median 

 flagellum and with articles shorter than those of 

 median flagellum. Anterolateral spine small, sharp. 

 Stylocerite acuminate, extending to or slightly 

 beyond midlength of first antennular segment. 

 Prosartema reaching to distal end of proximal 

 one-fifth of second antennular segment. 

 ANTENNAE 



Scaphocerite length 21^ times maximum width, 

 its lengtli relative to carapace length decreasing 

 slightly with growth; spine reaching base of 

 antennular flagellum. Carpocerite length ly^ times 

 width, extending slightly beyond base of eye. 

 Antennal flagellum relatively short, 1% c.l. 

 (fig. 41). 



WESTERN ATLANTIC SHRIMPS OF GENUS PENAEUS 



531 



