52 K. MITSUKUKI : STUDIES OX 



crossbars (shown by faint circles) connects it with tlic central rod. 

 The edge pieces are connected with tlie axis by live crossbars 

 which are in the level of the openings of the npper surface. The 

 openings between these crossbars are therefore alternate with 

 those of the upper surface. Textfig. 10b is one of those which are 

 very irregular. Textfigs. 10 c and d show the edge of two diflerent 

 ellipsoids, hi the textfig. 10 rf there is a departure from the common 

 type in that the openings in the middle are paired instead of all being 

 single. Textfigs. 10 e — g are from an individual which shows many 

 of tlie ellipsoids to be of a very simple structure. Here we have 

 to do with ordinary buttons with ridges on the middle piece. In 

 c, there art; two such ridges and from one of them an arch goes 

 over to one side. Such cases seem to show that tlie ellipsoids 

 are derived from l)uttons, but exactly how these are modified, 

 it is hard to say. It seems probable that the middle piece of the 

 button becomes the central rod of the ellipsoid. On each side of 

 the middle piece ridges, or rather scries of arches, are raised ; 

 then these are connected by lateral pieces with the edges. So 

 far it seems very plain ; but how tln^ double edges of the ellipsoid 

 are formed is not quite clear. If the edges of the cross-pieces 

 unite with each other and form an edge on each side of the 

 original button, there should be two series of openings instead 

 of one. It is ])0ssible that at first they are double and afterward 

 run together into one in the middle. The two paired openings on 

 the edge, shown in textfig. 10 r/, seem to point in this direction. 



This species is also cured for the market and exported to China. 

 In the prepared state there seem to ])e two varieties, probably 

 due to the diflerenccs in the color of the living animal. They 

 arc known under the names of " Shiro-Usa"' (PI. 111., fig. 23) and 

 " Kuro-Usa " (PI. 111., tig. 24). Their value seems to range from 



