17 



has a small pointed tubercle near the anterior margin. The lateral 

 plates are small and flat. The seminal receptacle is divided into two 

 cavities by a median septum (PI. VII, 5 B). The ostia to these cavities 

 are narrow and are found with difficulty. Moreover, the first joint of 

 the fourth pair of pereiopoda extends towards the median line and 

 borders the anterior margin of the thelycum. 



The petasma (PL VII, 5) is tube-like. The anterior end of the in- 

 ner lamina is kidney-shaped, while that of the outer lamina is turned 

 outward. The posterior end of the inner lamina is turned inward. 



We find a small, flat, somewhat oval spermatophore in the dilated, 

 extreme end of the ductus ejaculatorius. There is no appendage on 

 the spermatophore ; but we find a slender white mass of secretion in 

 the dilated portion. This white mass of secretion is often found at- 

 tached to the central plate of the thelycum after copulation (PL VII, 

 5 C). Hence this white mass seems to be homologous to the appendage 

 of spermatophores in other species. 



The color of the animal is yellowish or pale green with greenish 

 dots. The margin of the rhipidura is rich green. 



Females attain the size of 1 2 cm., males 9 cm. Pemales receive 

 spermatophores from the middle of Jul}'. The}' spawn from August 

 till October. 



The shell of young animals is quite naked, till they grow to the 

 length of about 6 cm. As the animal grows old, setae appear in 

 grooves or hollow parts of the shell. 



This species inhabits shallow parts of the bay or inlet only, always 

 in the depth of less than 20 metres. 



It is rather widely distributed from the Tokyo Bay to Formosa ; 

 but as its distribution is restricted to very shallow parts only, its catch 

 is not abundant. 



This species is often confounded with other different species such 

 as Penaens monoceros, P. velutinus, etc, as the original description is in- 



