HAWAIIAN AND OTHER PACIFIC ECHINI 



Collected by the U. S. Fish CoiNiMissrox Steamer "Albatross," 

 Commander Chauncey Thomas, U. S. N., Commanding. 



CIDARIDiE Miiller. 



Pedicellari^ are present in considerable numbers among the secondary 

 and miliary spines of the Cidaridoe and show the greatest diversity in thair 

 size, form, and relative abundance. We can distinguish in this family 

 three sorts of pedicellariae, differing from one another in structure, as well 

 as in size, and for convenience these have been designated as " tridentate," 

 " large globiferous," and " small globiferous." The three kinds are not, 

 however, sharply distinct from one another, for intermediate forms are 

 common, often on one and the same individual. Covered with their 

 epidermal tissue the pedicellarioB are difficult to study, but when the 

 organic matter has been cleaned off with caustic potash, or much better 

 with hypochlorite of soda, their calcareous parts show many interesting 

 features. In what follows, reference is made to these calcareous parts only. 



The tridentate pedicellarioB have the valves elongated, and either flat 

 or contracted rather abruptly into a slender blade, which may terminate 

 in a rounded, more or less smooth end, or in a conspicuous hook or *• end- 

 tooth." Each valve is practically solid and does not contain any interior 

 cavity, but it is often more or less perforated, near the base and along the 

 sides, with small holes. A tridentate pedicellaria is usually made up of 

 three valves, of equal size, connected with each other at the base by 

 muscles, and freely movable on the end of a stalk of variable length. But 

 similar pedicellariae with only two valves occur regularly in Porocidaris 

 purpurata, and rarely in P. variabilis, while in the latter species such 

 pedicellarice with four valves are also occasionally found. When closed, 

 the valves may meet for their entire length (and this is always so in 

 pedicellariae having two or four valves) or, as in many of those with three 

 valves, these meet only at the tip or for a fraction of their length, and are 



