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BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



In Figure 1 which is symmetrical and according to Ritter and Crocker's rule 

 three pairs of new rays have arisen successively on either side of A, the youngest 

 pair, adjacent to I and II, being c c. Ray one is slightly smaller than the other 

 primary rays. 



In specimen two (fig. 2) there are only five primary rays. Two pairs of new 

 rays have budded symmetrically with reference to A (or II, whichever it is). An 

 unpaired ray c restores the six symmetry, and may represent ray IV abnormally 

 suppressed during metamorphosis. Ray II is usually nearly opposite I, whence the 

 interpretation of the ray marked II in this specimen. 



Specimen three is asymmetrical. The interpretation of the rays is difficult and 

 it is not clear whether the ray marked A is homologous with that of A in Figures 1 

 and 2. Secondary ray a 1 is more nearly in the line of symmetry but if this is the 



Figs. 1-3.— 1, pycnopodia helianthoidesX2. young specimen with six primary rays showing symmetrical 

 budding of new rays on either side of ray a. madreporite shown in solid black; i-v, primary rays; a(l, 

 bb, cc, equivalent rays of pairs. 2, x 2. a young specimen with only five primary rays, the six symmetry 

 being restored by ray c, possibly equivalent to iv of fig. 1. two symmetrical pairs of new rays, qu, bb. 

 3. same, x 2. a primitively six, or possibly seven, rayed specimen in which new rays appear asymmetri- 

 cally and not always in pairs. a — iv, the usual axis of symmetry; d !-r-'v actual axis. rays have appar- 

 ently arisen in order (i, <2 ', 6, b ', c, d, € ; the last three certainly not paired. possibly m is equivalent 

 to d, which is usually opposite i; v would equal iv, and a would equal a "suppressed" v. then a and h, 

 which are large primary rays, may be interpreted as double a. d? the animal had lived new rays might 

 have appeared on either side of both a and ii; d ' may' represent such a beginning 



homologue of A, what is the primary ray marked A? Likewise ray III is in the 

 position proper to II. If it is II, what is the primary ray marked II, and why should 

 a ( = V in this case) be distinctly secondary in size? The smaller rays appear not to 

 have arisen in pairs but in the sequence a, a 1 , b, b ', c, d, e; d is obviously not con- 

 temporaneous with either c or e. 



In young specimens there are a few prominent abactinal spinelets, surrounded 

 by crossed pedicellariae, springing from subcircular, mostly isolated plates, between 

 which are tiny scattered spineless platelets imbedded in the skin. Papulae are 

 prominent, single or two to five in a group. 



Type-locality. — Sitka. 



Distribution. — Unalaska, Aleutian Islands, to San Diego, California; intertidal 

 in rocky situations, to 238 fathoms, sand. 



Specimens examined. — Thirty-two, in addition to numerous living and preserved 

 examples from Monterey Bay, Calif. 



