1 cm. 



FiGTTKE 41. — Penaeus (M.) aztecu^ aztecus Ives. Lateral view, 2 54.5 mm. c.l., off Corpus Christi, Tex. 



Figure 42. — Penaeus (M.) aztecus aztecus Ives. Sixth 

 abdominal somite, posterodorsal portion, 9 33.5 mm. 

 C.I., Ciudad del Carmen, Campeche, Mexico. 



shrimp change color while moving, becoming red- 

 dish, especially on the pleopods. 



Variations in the color of shrimps have been 

 attributed to several factors, such as temperature, 

 nature of bottom, and food. 



Distribution and Morphological Variations 



P. a. aztecus ranges from Martha's Vineyard 

 south to the Florida Keys and north on the west 

 coast of Florida to the northwest Sanibel grounds. 

 Apparently, it is absent north of these grounds to 

 the vicinity of Apalachicola Bay, where it appears 

 again, ranging along the northern and western 

 coasts of the Gulf of Mexico and the northwestern 



Figure 43. — Penaeus (M.) aztecus aztecus Ives. Dorsal 

 view of sixth abdominal somite, telson, and uropods, 

 S 37.5 mm. e.l., off Matagorda Bay, Tex. 



coast of Yucatan (fig. 49). The brown shrimp is 

 found farther north than other species of the 

 genus Penaeus occurring in tlie western Atlantic, 

 but it rarely reaches tlie nortliernmost waters of 

 its range. It seems to be a summer and early fall 

 visitor from Chesapealie Bay northward to 

 Martha's Vineyard; the northernmost breeding 

 population lives along the coast of North Carolina. 



534 



U.S. FISH AND WILDLIFE SERVICE 



