SHALLOW- WATER STARFISHES 55 



aa. Interactinal plates not so closely united; usually one or two rows, with 

 larger papular areas between. Major pedicellariae usually of but one 

 kind. Dorsal spines rather irregularly arranged, usually scattered, 

 sometimes areolate or acervate. 



b. Papular areas large, bearing numerous small papulae. Larvae are usually 



free-swimming brachiolariae ; genital pores dorsal. 

 Asterias, restr. Type, A. rubens L. 



bb. Papular areas smaller and bearing fewer large papulae. Eggs and larvae 

 are usually carried by the mother around the mouth. No free 

 larval stages ; genital pores ventral. 

 Genus, Leptasterias Ver. Type, L. mulleri (Sars). 



aaa. Interactinal plates lacking or rudimentary; papular areas large, numer- 

 ous. 



Parasterias, nov. Type, P. albertensis Ver., nov. 



DD. Dorsolateral plates and ossicles wide, irregular, rather closely joined, 

 leaving only small papular areas in longitudinal lines, but the 

 ossicles do not form regular rows. All the dorsal and marginal 

 plates are covered with close clusters of very small spines, longer 

 on the inferomarginal and interactinal plates. Autotomous; rays 

 mostly two or three to nine ; finally six in adult. 

 Stephanasterias Ver. Type, S. albula (Stimp.). Circumpolar; North 



Atlantic; Bering Sea. 



CC. Dorsal plates mostly rod-like. Interactinal plates small or rudimentary, 

 mostly spineless. Usually two kinds of major pedicellariae. 



c. Dorsal skeleton feeble, composed mostly of small, linear or roundish, iso- 



lated and reticulated ossicles. Dorsal spines few and mostly scat- 

 tered, but usually forming a median radial row. Both rows of mar- 

 ginal plates well developed and rather large, bearing single or 

 double rows of stout spines, separated by a wide lateral channel. 

 Dermal major pedicellariae large and abundant, wedge-shaped. 

 Minor pedicellariae abundant on the spines and skin, attached to a 

 large fleshy sheath on the spines. Alternate superomarginals with- 

 out spines. 

 Urasterias Ver. Type, U. linckii (Mull, and Trosch.). 



cc. Dorsal skeleton composed of nearly uniform short linear rods, irregularly 

 reticulated, and covered with numerous small, uniform spinules, 

 often in transverse rows or combs on the sides. Two rows of 

 marginal plates near together, in the type bearing double rows of 

 spines. Larger major pedicellariae obtuse, large. 

 Ctenasterias Ver. nov. Type, C. spitzbergensis (D. and K.). 



BB. The inner adambulacral spine, on alternate plates, is attached to the inner 

 edge of the plate, or within the groove. Peractinal plates feebly 

 developed or lacking. Dorsal spines small and numerous. 

 Alias terias Ver. Type, A. rathbuni V. 



H. ASTERIID^S OF THE NORTHWESTERN COAST OF AMERICA. 

 This faunal region contains a remarkable assemblage of the repre- 

 sentatives of this family. A few species from north of the Aleutian 

 Islands are of arctic or circumpolar origin, but most are endemic. 

 The most remarkable genus is Pycnopodia, strictly confined to this 



