BIOLOGY AND NATURAL HISTORY 199 



"any indication that these individuals have already spawned." He further 

 states that the disappearance of adults from the inshore waters is not suffi- 

 cient evidence to conclude that the life span is only one year. 



In 1939 Burkenroad published the results of field observations beyond 

 the range formerly investigated. He found white shrimp in water as deep as 

 40 fathoms and grooved shrimps in even greater depths. Shrimp taken in 

 deeper water were more than one year old and, in at least one specimen, 

 showed definite evidence of repeated spawning. Mating was found to bear 

 no close relationship to spawning, many impregnated females having 'Very 

 unripe" ovaries. 



King (1948), in describing the reproductive organs of P. setijerus, states 

 that the spawning season in Louisiana offshore waters extends from March 

 through September and that a single female may spawn more than twice 

 during that season. King also refers to unpublished manuscripts (by Lind- 

 ner, Anderson, and King, 1948) indicating that i)^ years is the age limit at 

 which one year-class can at present be distinguished from another. The 

 normal life span of the individual shrimp is a matter still undetermined. 



The information regarding the natural history of the grooved shrimps is 

 far less extensive than that for P. setijerus. Burkenroad's (1934) state- 

 ments about P. brasiliensis probably refer to P. aztecus. His later (1939) 

 findings seem to confirm this probability. Small individuals are found in 

 some abundance in coastal and inside waters in the summer. Larger indi- 

 viduals are taken offshore. The small inshore population is made up of 

 immature shrimp, males and females occurring in about equal numbers. 

 They are brownish-gray in color. Considerable size difference between the 

 sexes is evidenced in the offshore population, as is excess in the numbers of 

 females over males. The color of specimens from the outer littoral zones 

 tends to orange. Since the offshore males are all mature and since the size 

 difference between immature males and females is not as striking as is that 

 between mature animals, Burkenroad suggests a greater longevity for 

 female P. aztecus than for males. Again, there is evidence of repeated 

 spawning. The time of mating is correlated with the time of shedding, 

 females being impregnated while soft. 



The occurrence of P. aztecus off the Atlantic coast of southern New 

 Jersey during only September and October indicates (Burkenroad, 1939) 

 a "northward dispersal of juveniles and subadults from more southern areas 

 of spawning and metamorphosis, possibly followed by a successful return of 

 the maturing individuals." 



The only reference to the natural history of P. duorarum (Burkenroad, 

 1939) states that since only small, sexually immature adults are taken 

 inshore, the species probably "retires permanently to deeper water after a 

 littoral youth." 



