16 NATURAL HISTORY BULLETIN 



skeleton consists of lobed, wide, subimbricated or contingent 

 plates, arranged in three, five, or rarely more regular radial rows, 

 and sometimes with extra interpolated ossicles ; the rows are con- 

 nected by transverse ossicles. The principal plates bear, on a 

 central boss, large, isolated spines, usually making three or five 

 longitudinal rows above the marginal rows. 



Superomarginals are large, usually monacanthid, four-lobed; 

 the descending lobe is large and usually joined directly to the 

 inferomarginals. 



The inferomarginals are strong, convex ossicles, each bearing 

 usually two large spines. 



Uusually there is one row of interactinal plates, with or with- 

 out spines, closely united to the adambulacrals and inferomar- 

 ginals; sometimes they are rudimentary and without spines. 

 (Stylasterias.) 



Papulae are numerous and clustered. 



The lateral and dorsal major pedieellariffi are large, and are 

 usually of two or more forms. The larger are erect, wedge- 

 shaped, stone-hammer-shaped, or ovate, with the tips of the valves 

 wide and usually denticulate. Others are more slender, with the 

 valves spatulate or narrowed in the middle and the tips unguicu- 

 late, with interlocking teeth. Others similar, or smaller, with 

 acute tips, often occur on the adambulacral spines and margin. 

 Type, 0. columhiana V. 



This genus includes several large species on the North Pacific 

 coast. Off the eastern coast of the United States one species 

 (0. tanneri Ver.) is abundant at moderate depths, from south 

 of Cape Hatteras to southern New England. 



The subgenus Stijlasterias Ver. (op. cit., p. 48, 1914a), was sep- 

 arated mainly because it has only rudimentary and spineless 

 interradial plates, which are not visible without preparation. 



The following West Indian species belong to this group or sub- 

 genus. The young of 0. tanneri, when two or three inches 

 across, have the same features. 



Obthasterias subangulosa Verrill. 



Asterias angulosa Perrier, Bull. Mus. Comp. Zoology, vol. ix, p. 3, 1881; 



Mem. Etoiles de Mer, p. 202, 1884 {non Miiller.) 

 Ortliasterias (Stylasterias) suhangulosa Verrill, Starfishes N. Pacific Coast, 



pp. 168, 370, 1914a. 



