SHALLOW- WATER STARFISHES 133 



Superomarginals similar to the dorsals. Inferomarginal spines a 

 little longer, usually in frNvo or three rows. Peractinals in one or 

 two rows. Adambulacral spines diplacanthid. 



Minor pedicellaric-e usually numerous. Frequently, but not in all 

 varieties, nor in the young, there are a few very large, stout, stone- 

 hammer-shaped or wedge-shaped serrate dermal pedicellariae on the 

 sides of the rays or on the interradial spaces beneath. 



Its known distribution is from Vancouver Island to Yakutat and 

 Dutch Harbor, and St. Paul's Island, Alaska. It is abundant 

 between tides on rocky shores and in shallow water. 



Owing to its great variability, especially in the dorsal spines, it 

 seems to me desirable to distinguish several named varieties, which 

 are described below. The varieties often appear as different as dis- 

 tinct species. 



The oral spines in this species are more feebly developed than in 

 most of the allied forms, but vary considerably. The peroral spines 

 usually consist of only two rather short apical ones on each jaw, 

 usually distinctly stouter than the adorals, usually straight, but 

 sometimes curved a little toward each other, so that their tips are 

 convergent. The small side-spines are generally lacking and replaced 

 by a pedicellaria, but in some of the larger specimens it is present 

 on some of the jaws and not on others ; when present it is small and 

 short, acute, not more than one-third or one-fourth the length of the 

 apical pair, but it is variable. 



The epioral spines are rather longer and more slender than the 

 perorals, and like the adorals in form, though a trifle longer. It often 

 happens that one of a pair is lacking on some of the jaws and then 

 the single spine stands nearly in the middle of the jaw. The adoral 

 carina consists of three contingent pairs of adoral plates, besides 

 the epioral ; their single spines are decidedly more slender than those 

 more distal, and are a little longer. Double rows of spines usually 

 commence on the fifth to the eighth plate. 



The normal young of this species, when lo mm. to 15 mm. in 

 diameter, have a rather openly reticulated dorsal skeleton, composed 

 mostly of deeply lobed ossicles, with three or four unequal lobes. 

 When 20 mm. to 25 mm. in diameter, they usually have the char- 

 acteristic spinulation of the adults, though the spines are smaller and 

 much less numerous, and the median radial row is very distinct and 

 pretty regular. The papulae are few and mostly stand singly. The 

 madreporic plate is small, with but few gyri. The superomarginal 

 and inferomarginal plates are well defined and each bears a single 



