ASTEROIDEA OF NORTH PACIFIC AND ADJACENT WATERS FISHER. 



59 



Actinal interradial areas very small, paved with eight to twelve paxilliform 

 plates, sometimes even fewer, the spinelets being similar to those on adjacent parts 

 of the inferomarginals — i. e., slightly tapering, terete or flattened at tip, and skin 

 covered. In specimens with very spiny superomarginals, the actinal intermediate 

 paxillse usually bear one or occasionally two stout tapering spines, surrounded by 

 the smaller spinelets. Many specimens do not have this spine. Actinal inter- 

 mediate spines are strongly developed in a large specimen from San Diego, from 

 which the diagnosis is drawn. 



Superambulacral plates well ileveloped. Under edge of ambulacral ossicles 

 normal, and smooth, not produced into a thin lamina between consecutive ampullae, 

 nor toothed in any way. Gonads a.xillary. Si.x Polian vesicles, two in the inter- 

 radius containing tlie madreporic canal (one on either side of it), and one in each 

 of the other four interradii. 



Madreporic body large, exposed, 5 to 6 mm. in diameter (in big examples), 

 the adcentral edge about midway between center of liisk and edge of marginal 

 plates. Striations very irregular often with tin}" protuberances along ridges, these 

 sometimes fusing after the manner of the central granules of the paxillse. 



Variations. — This species, as has already been said, varies greatly, not only 

 in respect to many details of ornamentation but also as regards dimensions, the 

 relative size of rays and disk, and the width of paxillar area. It is not surprising, 

 therefore, that the general appearance should also differ considerably, according 

 as the T&ys are long or short, or the superomarginals encroach considerably upon 

 the paxillar area, or as the latter are very spiny or not, or as the inferomarginals 

 extend laterally bej^ond the superomarginals. If one encountered the isolated 

 extremes he would certainly be justified in regarding them as examples of distinct 

 species. It is not at all improbable that several species now regarded as distinct 

 may reaUy belong to this variable species. The character of the paxillae and of 

 the inferomarginal armature appears to be more stable than that of the marginal 

 plates and is hence more valuable in an offliand determination of specimens. 



A few specimens have been analyzed to show some of the more obvious differ- 

 ences or variations. 



Table showing variations in Astropecten armatus. 



Locality. 



San Diego. 



Number 

 of supero- 

 mar- 

 ginals. 



5.1:1 

 4.3:1 

 3.4:1 



Upper row of superomar- 

 ginal spines present. 



Lower row present. 



1 or 2 spines 6 



3 or4spines6 



5or Gspinesb 



3 or 4 tubercles*., 

 1 spine* 



Infero- 

 marginals 

 extend he- 

 yond super- 

 omarginals. 



Scattered spines. . 



Widtli of 

 paxillar 

 area, base 

 of ray. 



a Absent, from terminal Qfth of ray. 



6 Xt base of ray. 



: Absent from first five or six plates. 



The smallest specimen of this species I have seen has 11 = 17 mm. and a few 

 enlarged superomarginal tubercles. The central spiuelet of paxillae is granuliform 



