MACRURA. 69 



Penaeus monodon, Fabricius. 



Penaeus monodon, Fabricius, 'Suppl. Ent. Syst.,' p. 408, 1798. 

 Penaeus semisnlcatns, de Haax, ' Fauna Japonica,' p. 191, 1849. 

 Penaeus carinatns, DANA, ' U.S. Expl. Exp.,' p. 602, 1852. 



Locality : Palk Strait (Station XVIII.), several specimens. 

 Measurements of two males and two females : 



From end of telson to 



Males. Females. 



rom end ot telson to "] .... .... 



> 162 millims., 131 millims. 195 nullims., 135 millims. 



tip ot rostrum . . J 



Length of carapace 1 

 and rostrum . . J 



52 41 60 43 



Both male and female specimens possess a well-marked median groove extending 

 from behind the rostrum to the posterior end of the carapace. Spence Bate found 

 this groove absent in the single male which he examined. There is no doubt that 

 the position of the ventral rostral teeth relative to the upper rostral teeth is subject 

 to variation. 



General distribution : India, Ceylon, Singapore, Japan, Pacific and South Africa. 



Penseus indicus, Milne-Edw. Plate I., fig. 1. 



Penaeus indicus, Milne-Edw., ' Hist. Nat. Crust.,' II, p. 415, 1837. 



(?) Penaeus merguiensis, he Max, ' Journ. Linn. Soc.' (Zool.), vol. 22, p. 287, 1888. 



Locality: Gulf of Manaar (Station XLIX.), 5 specimens. Lengths varying from 

 14 millims. to 40 millims. All immature. 



The rostrum in these specimens differs from the type species and has a formula 



* . The anterior half of the rostrum bears no teeth dorsally. The rostrum 



6 J 



is very slender and extends in front of the antennular peduncle a distance equal to 

 half the length of the peduncle. In spite of these differences from the type species, 

 I have referred these specimens to the above species, because there seems to be little 

 doubt that the rostrum is subject to a great deal of variation in this form. The 

 " Challenger " specimens differed in the form of the rostrum from Milne-Edward's 

 species, and de Man's species, P. merguiensis, appears to differ in no important 

 respects from P. indicus. 



An examination of the various forms grouped together under this species would be 

 valuable and instructive, and would throw some light on the value of the rostrum in 

 classification. 



General distribution : India, Philippines, Mergui (?), Ceylon. 



