K 



\1 



Figure 40. — Pcnaeiis (M.) az- 

 tecus azteciis Ives. Oephalo- 

 thorax, 9 47.5 mm. c.l., off 

 Tampico, Tamaulipas, Mexico. 



attached border with elongpted, narrow patch of 

 14 to 25 small, closely set teeth arranged in two 

 or three series; apex of costa not projecting free 

 but tightly joined to adjacent membranous i^ortion. 

 Ventrolateral lobule with extensive armature of 

 rather closely set spines. Distal fold relatively 

 small, armed with 2 to 33, pei-haps more, spinules, 

 occasionally unarmed. Distomedian projections 

 rather thick and short, slightly overhanging dis- 

 tal portion of ventral costae. 

 APPENDIX MASCULINA (fig. 46 e) 



Eather elongated, its length 1% to 1% width 

 at base, armed with single row of short, strong 

 spines along distal four-fifths of lateral margin, 

 and with longer spines along median margin. An- 

 terior surface slightly convex, posterior surface 

 with rather deep excavation flanked by sharp lon- 

 gitudinal ridge projecting from median margin. 

 THELYCUM (figs. 47, 48) 



Anterior process terminating ventrally in sharp 

 semicircular to nearly triangular ridge, surround- 

 ing concave surface usually plain, although some- 

 times with knob or short rib at center; posterior 

 process with median carina typically bifurcate an- 

 teriorly, forming two ribs; ribs turning mesially 

 and almost coming together at anterior process, 

 giving rise to diamondlike or ovate-acuminate 

 structure; depression thus formed deep when ribs 

 are high or vei-y shallow, when ribs are low, 

 usually plain but sometimes bearing median rib 

 along anterior or posterior half, rarely along en- 

 tii-e length. Lateral plates with anteromedian 

 angles widely divergent leaving posterior process, 

 including median carina, ex^josed. 



COLOR 



Although of variable color, P. a. aztecus is most 

 frequently brown. Thus, the commercial name of 

 brown shrimp or brownies in the United States and 

 camaron cafe or camaron moreno in Mexico. Large 

 offshore individuals often have an orange or lemon 

 coloration, deeper on pereopods and around tail- 

 fan ; the latter often has a darker edge which may 

 be purple or reddish purple. Juveniles and sub- 

 adults are frequently light grayish brown or brown 

 with darker speckles on the sides; red and green 

 specimens also occur and are commonly called red 

 shrimp and green shrimp. P. a. aztecus occasion- 

 ally has a lateral spot at the junction of third and 

 fourth abdominal somites, in this character it re- 

 sembles both subspecies of P. duoraim/tn and also 

 P. iras'die-nsis. Fishermen believe that brown 



WESTERN ATLANTIC SHRIMPS OF GENUS PENAEUS 



533 



