2 HAWAIIAN AND OTHER PACIFIC ECHIXI. 



more or less widely separated above their basal union. In size, the valves 

 show a wide range, from less than half a milHineter to over half a centi- 

 meter long, the width being from .10 to .70 of the length. In small 

 examples the stalk, which is a simple, straight rod, is often as long as 

 the valves, but in large ones the valves are much the longer. Tridentate 

 pedicellariae occur mainly around the primary spines, especially on the 

 actinal half of the test, but they may occur abactinally and are sometimes 

 conspicuous on the abactinal system. They may be entirely wanting not 

 merely in individual cases but in whole groups of species. 



The large globiferous pedicellariae are always three-valved. They take 

 their name from the fact that when the valves, which are large and hollow, 

 are closed in their normal position, the whole head appears more or less 

 globular. The cavity of each valve opens on the inner side near the tip, 

 or the opening may be terminal. The size of the opening is very variable, 

 but the three valves of any one pedicellaria are all alike. When the 

 opening is not at the end, the tip of the valve may be blunt and rounded 

 or it may terminate in a more or less conspicuous " end-tooth." When 

 the opening is large the edges are usually irregularly serrate, and more 

 or less of the entire length of the margin of the valve may be provided 

 with small teeth. The lower edge of the opening is usually sharply 

 indicated by a horizontal, outwardly curved "lip," but this is frequently 

 imperfect or entirely wanting. The lower part and back of the valve is 

 more or less perforated with holes of variable size and shape. True large 

 globiferous pedicellariic show relatively little diversity in size, the valves 

 ranging only from one-half to a little more than one millimeter in length. 

 The stalk is usually about as long as the valves, but is often less, while 

 on the other hand it may be twice as long. Usually it is a simple, straight, 

 calcareous rod, but in .some species there are frequently, if not always, 

 projecting, slender spicules which form a circle near the distal end of the 

 stalk; this is referred to as the "limb." Large globiferous pedicellaria) 

 occur chielly on the abactinal half of the test and most comuionly between 

 the priuiary spines, though they are often frequent on the abactinal system. 

 Thoy seldom oocm- on tiie ambulacra or near the actinostome and they are 

 often entirely wanting, not merely in individual cases, but even in whole 

 groups of species. In individuals on which they are abundant, there may 

 not micommonly be found large globiferous pedicellaria^ in which the 

 valves have become elongated and narrow, without a lip, and the opening 



