1918 Bush: on Echinoderms 23 



DD. Adambulacral spines alternating 1 and 2 to a plate. 



EVASTERIAS (p. 23) 



CC. Interactinal spines usually in 1 row with 1 or 2 short rows 

 near disk. asterias (p. 25) 



BB. Dorsal spines in 3 to 7 rather regular rows. 



ORTHASTERIAS (p. 25) 



AA. Rays 6 (rarely 5). leptasterias (p. 26) 



AAA. Rays 20 to 24. pycnopodia (p. 28) 



Genus Pisaster 



Disk thick, rather large; rays 5 or 6. stout. Dorsal ossicles strong, 

 numerous, not confined to 3 or 5 rows ; dorsal spines forming a net, or 

 irregular; upper marginals distinct or not; lower marginal and actinal 

 plates and spines numerous, crowded; adambulacral spines in 1 row, 1 to 

 .1 plate; peculiar major pedicellariae sessile, large, thick, ovoid or wedge- 

 shaped in appearance specially lateralh^ and ventrally. Ambulacral feet 

 usually in 6 rows. 



Hybrids between the 2 species mentioned below are common. In 

 some the principal characteristics of P. confertus may occur, but spines 

 of the large P. ochraceus type may also appear. The arrangement of the 

 spines may also vary somewhat. 



key to species 



A. Dorsal spines unequal, large, strongly capitate. 1. P. ochraceus 



AA. Dorsal spines equal, small, not strongly capitate. 2. P. confertus 



1. Pisaster ochraceus (Brandt) A. Agassiz. 



Asterias ochraceus Brandt; Asterias janthina Brandt; Asteracan- 

 thion margaritifer Miiller & Troschel. 



Dorsal spines arranged net-like but sometimes with wide areas and 

 sometimes with groups where the lines intersect, forming a conspicuous 

 central pentagon and sometimes partial median rows ; spines coarse, stout, 

 strongly capitate, very unequal. — Abundant, along the tide line. 



2. Pisaster confertus (Stimpson) Veri'ill. 



Dorsal spines small, numerous, not strongly capitate, acute or clavate; 

 arranged in a close network with or without median radial rows and cen- 

 tral pentagon, without noticeable groups. 



Genus Evasterias 



I'orms large; rays long, tapering gradually; disk small. Dorsal 

 skeleton usually firm ; ossicles small, lobed ; dorsal spines numerous, 

 arranged net-like or irregularly or in short transverse rows; marginal and 



