They are 1 2 cm. in length. 



This species is closely related to the group of P. affinis ; but dif- 

 fers from it by the armature of the tail segment. 



PENAEUS TENELLUS. 



(PI. VI, 2) 



Penams tenellus, Sp. Bate, Challenger Rep. Crust. Macrura (1888). 

 Penacus cnicifcr, Ortmann, Zool. Jahrbuch. Abth. Syst. (1890). 



The shell smooth and naked. The rostrum shorter than the 

 peduncle of the first pair of antennae, 8 dentate. The gastric tooth 

 wanting. No median kiel in the carapace. From the orbit, a longi- 

 tudinal fissure runs towards the posterior margin, but disappears 

 before reaching it. The second joint of the first and second pairs of 

 pereiopoda unispinose. The pleon is carinated from the fourth somite 

 backward. The tail segment has a shallow and narrow channel. 



The central plate of the thelycum (PI. VII, 8 A) is large, lozenge 

 shaped and is longitudinally grooved. The lateral plates are united 

 into one piece. The seminal receptacle consists of two small entirely 

 separate cavities (PI. VII, 8 B). 



The petasma is thin and broad, has a pair of transverse horns 

 (PL VII, 8). 



The color is light brown with numerous brown spots which form 

 indistinct bands. The antennae, pleopoda and the margin of the 

 rhipidura are reddish. 



The female specimen attains the length of 7.5 cm., while the 

 male is a little smaller. 



This species is found rather abundantly in the Inland Sea. Rough- 

 ly speaking it is distributed along the lower half of our empire. 



Known under the names of "sakurayebi," "a'kazayebi," "gaseyebi," 

 etc. 



