176 



ARGONAUTA FlîOM TEIlTIAllY. 



they are also arranged in longitudinal lines. Besides it shows no 

 distinction of ribs and intermediate riblets. Each of the prominences 0:1 

 the keel is continued to a ridge which is usually directed backwards from 

 the aperture. The ridge is sometimes divided into two low tubercles. 

 The tubercles on the lateral edge are neither numerous nor prominent. 

 The shell of the older individual measures only 3.2 cm. in width, thus 

 being narrower than those of A. tuberculosa. The general outline of 

 the shell, the size of the whorls near the center, the rows and numbers of 

 ribs, therefore can distinguish our species from A. tuberculosa. 



In Japan we find only the following species of argonants : 



1. A. argo, Linné, from Tokyo Bay, Misaki in Sagami, and 

 Tokunoshima in Osumi. 



2. A. hians Sol., from Misaki, the Inland Sea, and Kiire in 

 Satsuma. 



3. A. owenii Ad. and Eve., from Niijima in Idzu. 



4. A. bôttegeri Maltzan. 



It seems therefore very interesting, that the tuberculated form is widely 

 spread in warm sea but has never yet been found living in Japan, though 

 having there its representative as a Tertiary fossil. 



