is 



This species closely resembles P. monodon {P. semisulcatus) and is 

 often confounded with it, but differs from the latter by the shorter 

 flagrellae of the first antennae and also in the minute structure of the 

 petasma, color, etc. 



PENAEUS MONODON. 



(pi. n, i) 



Penactis monodon, Fabricius, Suppl. Ent. Syst. (1798); M-Edw., 

 Hist. Nat. Crust. (1837). 



Penaeus semisulcatus, de Haan, Fauna Japon. Crust. (1849); Miers, 

 Proc. Zool. Soc. p. 299 (1878). 



The shell thick and polished. The rostrum slightly curved, about 

 2/3 time as long as the carapace, 7 or 8 dentate above and 3 dentate 

 below. The flagellae of the first pair of antennae are as long as the 

 peduncle. The dorsal median carina of the carapace becomes gradually 

 low and less distinct as it approaches the posterior margin of the 

 carapace and disappears before reaching it. Generally the carina is 

 not grooved. When it is grooved, the groove is very faint. The 

 lateral grooves are lost near the gastric tooth. The first pair of the 

 pereiopoda is bispinose, the second pair unispinose. 



The seminal receptacle (PI. VII, 4 A) is almost the same as that of 

 P. ashiaka. The outline of the thelycum is oval and its central plate 

 is larger than that of P. ashiaka. 



The petasma (PI. VII, 4) closely resembles that of P. ashiaka in 

 the general appearance. The distal end of its anterior end is pointed 

 and near that point we find a few minute teeth. Btit this part is con- 

 cealed under a soft membrane. 



The color of the animal is dark brown or rarely blackish. Dar- 

 ker and lighter shades of color alternate each other thus giving 1 the 

 animal the banded' appearance. 



