HAWAIIAN AND OTHER PACIFIC ECHINI. 



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

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



CIDARIDiE Muller. 



Pedicellari^ are present in considerable numbers among the secondary 

 and miliary spines of the Cidaridas and show the greatest diversity in their 

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

 three sorts of pedicellaria?, 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 pedicellarioe 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 pedicellari;T3 have the valves elongated, and either flat 

 or contracted rather abruptly into a slender blade, Avhich 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 pedicellarias with only two valves occur regularly in Porocidaris 

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

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

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

 pedicellarias having two or four valves) or, as in many of those witii three 

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



