JAPANESE ASTEROIDEA. 641 



Besides these two series there may be a few very short but com- 

 paratively thick spines on the actinal surface of the mouth-ijlates, 

 between the second row of spines of either side (PI. XIX, fig. 

 274). The mouth-plates are usually separated from the adam- 

 bulacral and ventrolateral plates by a groove. 



Ventrolaterals. — When denuded of the spines the ventro- 

 lateral plates are hregularly polygonal in outline, slightly imbrica- 

 ting, quite firmly ankylosed with one another, and presenting each 

 a convex surface on the actinal side. The plates are largest 

 near the mouth and ambulacral furrows, and those of the arms 

 and vicinity of the disk margin are exceedingly small. Each 

 ventrolateral j^late bears a comb-like row of somewhat flattened, 

 pointed spines, of which the number may vary from nine or ten 

 on a very large plate to about four on the smallest plates and 

 those of moderate size. On the smaller plates these spines are 

 regularly arranged in one row, but on the larger ones some of 

 the spines may depart from the row, so that two rows may oc- 

 casionally be found on some plates (PI. XIX, fig. 274). 



Dorsal lolates. — Along the margin of the disk and arms there 

 is a band-Hke portion on the dorsal side, in which the plates 

 are all of the same form and nearly equal size, each plate being 

 either rounded or lozenge -shaped in outhne, and bearing each 

 from six to a dozen granuliform spinelets. In the remaining 

 parts of the dorsal side there are two orders of plates according 

 to their size, which may be called, for the sake of description, 

 principal and accessory. The principal plates are larger and are 

 either elongated or crescent- shaped in outhne. Around the centre 

 of the disk the principal plates are arranged somewhat concen- 

 trically, with the concavities of the crescent- shaped plates turned 



