70 HAWAIIAN AND OTHER PACIFIC ECHINI. 



lixula. The valves (fig. 15) are broad, rounded at the tip, and often have a 

 marked notch on each side just above the base; they range from .25 to 

 1 mm. in length. 



The ophicephalous pedicellariaB resemble those of piiiictiilata, and cannot 

 be certainly distinguislied from them. The heads of the stalks (fig. 18) are, 

 however, not constricted. 



The triphyllous pedicellariae are rare. They have very broad valves 

 (fig. 16), about .25 mm. long, and are difficult to distinguish from the smallest 

 tridentate pedicellariae. 



The calcareous particles in the pedicels (fig. 17) resemble those of piinc- 

 tidata, but are stouter and rougher. Those of the gills are also similar to 

 those of pundulata, but are remarkable for the fact that they often carry 

 pedicellariae. 



The sphaeridia (fig. 19) are like those of punctulata. 



Arbacia lixula Loven. 



Echinus lixula Linnseus, 1758. Sys. Nat., p. 664. 

 Arbacia lixula Loven, 1887. Ech. desc. by Linn., p. 112. 



Plate 48, figs. 10-U. 



The tridentate pedicellariae are very variable in size and number, but are 

 generally small, and actinal in position. The valves are very wide in pro- 

 portion to the length, which ranges from .25 to .05 mm. ; they may be 

 bluntly pointed (fig. 10) or more or less rounded at the tip (figs. 11 and 12). 



The ophicephalous pedicellariae are common, especially actinally. The 

 valves (fig. H) are much narrower than in pwiciulata and less rounded at 

 the tip. They measure about .50 mm. in length, while the stalks are 2 or 

 3 mm. long. The heads of the stalks are often somewhat constricted as in 

 punchdata. 



The tripliyllous pedicellariaB are very scarce. The valves (fig. 13) are 

 considerably more constricted than in pundulata. 



Calcareous particles in the pedicels are like those which occur in punctu- 

 lata, but the perforated plates in the gills are more like those of Dufrcsjiii. 



The yphtvjridia are like those of pundulata. 



