190 



BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



Variations.— This is a variable species both in respect to shape and details of 

 ornamentation, particularly in the size of paxillae. The last variation seems to be 

 correlated with the character of the bottom. 



The extremes in body form are best appreciated from the photographic figures, 

 and range from a short broad-rayed almost arcuate-pentagonal shape (which is 

 unusual) to one with smaller disk and longer, distally attenuate rays. The follow- 

 ing table will give an idea of the differences: 



Next to the shape the size of paxillae is most noticeable in variability. The 

 extremes have been noted in the foregoing description. Specimens with small 

 spaced paxillae are from hard sandy bottom; those with larger and more closely 

 placed paxillsc (as, for instance, the specimen mentioned from station 4367) are from 

 soft mud. The large paxillte evidently are a protective device for the papulffi, prevent- 

 ing their being clogged with mud. The danger of such an event is very slight on hard 

 sand or shells; hence the partial atrophy of the paxillar crown in specimens from 

 such a substratum. Unfortunately the type is not so typical in regard to paxillse as 

 the variety with more closely placed and slightly larger ones. The specimen from 

 station 4367 is extreme. (See figures.) 



There is variation in the width of superomarginals, and in the degree in which 

 they encroach on paxillar area. This gives a slightly different appearance to 

 abactinal paxillar area. Small variation occurs in the number of transverse rows 

 of granules, as well as in the length of inferomarginal spinules. Variations in 

 occurrence of pedicellariie and in adambulacral armature have already been 

 mentioned in the description. 



Young. — Numerous very small specimens from stations 4433 and 4533 are easily 

 recognizable as Pseudar chaster. R = 5 mm. Paxillse have one to four spinelets; 

 superomarginals seven; terminal plate large with two spinelets; one very prominent 

 inferomarginal spine, forming longitudinal series all along ray; adambulacral plates 

 with three furrow and two to four much shorter actinal spinelets; the median un- 

 paired tooth of mouth plates very prominent. The conspicuous inferomarginal 

 spine with several associated spinules projecting out from side of ray is very 

 characteristic. 



Type.— Cut. No. 22335, U.S.N.M. 



Type-locality. — Albatross station 4423, between Santa Barbara and San Nicholas 

 Island, California, 216 to 339 fathoms, shells, black pebbles, green sand. 



Distribution. — North of Monterey Bay, California, to Los Coronados Islands, 

 Lower California, and from 54 to 382 fathoms. 



