SHALLOW-WATER STARFISHES 183 



Adambulacral spines are irregularly diplacanthid, small, slender, 

 terete or obtuse, about half as long as the inferomarginals and 

 scarcely one-third as thick. The outer ones are a little longer and 

 often slightly clavate; the proximal ones become distinctly longer and 

 more tapered. There is an unusually wide naked space between the 

 adambulacral and the inferomarginal spines. 



Oral and epioral spines longer and distinctly stouter. 



Remarkably large dermal major pedicellariae are sparingly scat- 

 tered over the back and sides. They are mostly of two forms ; the 

 larger are stout, erect, compressed, ovate, with a stout base, often 

 nearly as thick as the adjacent spines ; apex a little acuminate, obtuse. 

 The others are about as long, but not so stout, compressed, con- 

 tracted in the middle, with the blades a little spatulate and dentate 

 or unguiculate at the tips. Much smaller, simple, lanceolate ones 

 also occur. Thick wreaths of rather large minor pedicellariae sur- 

 round the basal half of the dorsal and superomarginal spines ; on the 

 inferomarginal spines they form secund groups. 



The madreporite is rather prominent, with very fine g>'ri ; it is not 

 surrounded by special spines. 



The color, as dried, is dark purplish or greenish brown above ; pale 

 yellowish below ; madreporite pale lemon-yellow. 



The smaller specimen agrees well with the larger, except in having 

 all the spines disproportionately smaller, and in lacking visible per- 

 actinal plates and large dorsal dermal pedicellariae ; but similar ones 

 occur beneath, on the interradial areas. Minor pedicellariae form 

 large wreaths on the dorsal spines. 



Two specimens (No. i8) were dredged in shallow water in 

 Departure Bay, British Columbia, by Prof. John Macoun and party, 

 of the Canadian Geological Survey, in 1909. 



These specimens are probably both young, though the larger is 

 nearly as large as the type of 0. kahleri, with which it appears 

 nearly to agree in proportions. It may, possibly, be the young of 

 O. Columbiana, which comes from the same district ; but the smallest 

 undoubted specimens of that species that I have seen have much 

 stouter rays and much larger and less numerous spines, though the 

 rays are scarcely longer, and it has a row of spiniferous peractinal 

 plates. The large dermal dorsal pedicellariae are similar in the two 

 forms, but relatively smaller and less stout in the young columbiana. 

 The minor pedicellariae are also smaller in the latter and form 

 smaller wreaths on the dorsal spines. Therefore it is more probable 

 that they are distinct, though closely related species. It would 

 certainly be unwise to unite them without intermediate forms. 



