IQ C. ISHIKAWA. 



both the forms carry eggs, showing thus they are both sexually mature ; 

 moreover each form lives separately as Mr. Sakai informs me. The close 

 examination of the two reveals me of no difference, so that it is quite certain 

 that there exist two different forms of the same species existing in one and 

 the same district, but each keeping its own colony. A few specimen was 

 found in the bottle containing a species of Estheria from Kano, in the 

 province of Mino. This last is exactly of the same size as our smaller 

 specimen. 



ESTHEEIA GIFUENSIS, n. spec. (PL V.). 



Shell valves thin, amber coloured oblong-oval, about two-thirds as 

 broad as long, the anterior edge more rounded than the posterior. The beak 

 small but rather projiiinent, situated at about one-fourth from the anterior 

 edge of the shell ; the dorsal edge behind the beak quite straight till to the 

 posterior fourth of the shell, where it suddenly slopes down. About fifteen 

 to seventeen lines of growth, with a row of coarse setae along the seven or 

 eight marginal lines. Another row of smaller and denser setfe at the edge 

 of the shell, situated a little beyond the larger ones, the tips of these larger 

 setfe at the edge of the shell being hooked (fig. 10). The supporting pillars 

 situated in the cellular matrix of the shell appear as fine punctuations under 

 a low magnification. Under a high power these punctuations appear as 

 star-shaped figures as has been observed by various other authors. These 

 star-shaped structures disappear along the free edge of the shell, where a 

 number of clear oval or irregular markings are to be seen. The outermost 

 of these form a single row at some distance from the edge of the shell and 

 running parallel with it. The other markings are either scattered irregularly, 

 or arranged in parallel rows and confluent with the outermost ones. These 

 are also found along all the lines of growth, but less distinctly. 



The male shell slightly narrower than the female (comp. figs. \a and 2a.) 

 the dorsal edge posterior to the beak straighter, and forming an angle with 

 the posterior curvature of the shell. The dextro-sinistral diameter of the 

 shell slightly less than in the female. 



Male (fig. 1) :— Head not very large. The first antennoo (fig. 5) reaching 



