Figure 12. — Penaeus aztecus Ives. A, anterior portion of 

 animal in lateral view, "Form A" from North Carolina, 

 natural size: B, petasma of adult male, distal portion, 

 view from right side ; C, thelycum of adult female ; B-C, 

 1 mm. indicated (after Burkenroad, 1939). Chromato- 

 phore distribution in tail fan (semidiagrammatic) of 

 D, 17 mm. juvenile, E. 32 mm. juvenile; D-E, approxi- 

 mately X 5 (after Williams, 1953). 



terior tooth remote from others, anterior 6 or 

 7 on rostrum proper. Lower margin of rostrum 

 with two or three teeth, tip slender, horizontal, 

 or directed slightly upward, unarmed. Anterior 

 margin of carapace with strong antennal spine 

 on carina extending backward nearly to well- 

 developed hepatic spine. Cervical groove extending 

 halfway from hepatic spine to dorsal carina. A 

 subhorizontal suture below hepatic spine, and a 

 groove extending from near hepatic spine to near 

 base of ocular peduncle. An orbital ridge be- 

 hind eye. 



Female with thelycum composed of two broad 

 lateral plates and a median plate. Posteromedian 

 part of median plate variably ovate-acuminate in 



outline with tip raised into a short posterior carina 

 diverging anteriorly into raised margins. Ventral 

 surface concave; broad anterior end of posterior 

 part merging into concave, triangular or semi- 

 circular anterior portion. Lateral plates produced 

 medially to meet in midline except diverging to ex- 

 pose median plate. 



Abdomen with segments four to six carinate, 

 carina of sixth flanked on each side by a narrow 

 groove. Telson with deep median groove and an 

 acuminate tip. Petasma of male with distoven- 

 fcral lobes not projecting free of distolateral lobes ; 

 with several compact series of short, crowded 

 spines near distal ends; a fold of free margin 

 of distolateral lobe beyond end of distoventral 

 lobe bearing moderate spinose armature. 



Measurements. — Length of body: large male, 

 162 mm.; large female, 211 mm. 



Variations. — Burkenroad (1939) divided this 

 species into "Forms," "A," "B," and "C." The 

 chief differences are summarized here. 



In "Form A," the grooves lateral to the dorsal 

 carina are well denned posteriorly and are dis- 

 tinctly broader than the carina. The carina is 

 distinctly and continuously grooved. The dorso- 

 lateral grooves of the sixth abdominal segment 

 are broadly open, their width "being from three- 

 fourths to equal the interval between their dorsal 

 lip and the midline." 



In "Form B," the grooves lateral to the dorsal 

 carina are usually much narrower than the carina 

 and tend to be ill defined posteriorly. The dorso- 

 lateral grooves of the sixth abdominal segment 

 "range up to one-half as broad as the interval 

 between their dorsal lip and the midline, and 

 the dorsal lip is frequently low and ill denned." 



In "Form C," the grooves lateral to the dorsal 

 carina are much as in "Form A," but the carinal 

 groove is shallow and frequently interrupted by 

 plane intervals. The dorsolateral grooves of the 

 sixth abdominal segment are extremely narrow, 

 "their width less than a third of the interval 

 between their dorsal lip and the midline, and are 

 sometimes entirely closed." 



The rostrum is relatively shorter and deeper in 

 old individuals than in young ones. In unworn 

 adults, it reaches to or beyond the middle of the 

 third antennular article. In young adults, it may 

 reach the end of the antennal scale. The rostrum 



MARINE DECAPOD CRUSTACEANS OF THE CAROLINAS 



25 



