24 Pub. Puget Sound Biol. Sta. Vol. 2, No. 33 



interactinal plates stout, lobed, joined firmly in longitudinal rows, each 

 plate bearing 1 or more long spines. 



Hybrids in this genus are common. Perhaps the most common cross 

 is one with the dorsal spines like the slender E. acanthostoma type and 

 the ventral spines like the E. troschelii. The dorsal spines may be partly 

 of the thicker E. troschelii type and partly of the slender E. acanthostoma 

 type. Some specimens are found which look like Evasterias but which have 

 a feebly developed dorsal skeleton and unusually scattered spines. These 

 seem to be a cross between some species of Evasterias and of Orthasterias. 



KEY TO SPECIES 



A. Dorsal spines arranged net-like or clustered ; interactinal spines i to 

 6 rows. !■ E. troschelii. 



B. Dorsal spines arranged net-like. 



C. Dorsal spines in a rather large-meshed net-work. 



la. E. troschelii rudis 

 CC. Dorsal spines in a small-meshed net-work. 



lb. troschelii densa 

 BB. Dorsal spines arranged not net-like but conspicuously clustered. 



Ic. E. troschelii subnodosa 



AA. Dorsal spines not arranged net-like but often in transverse rows; 



interactinal spines more than 6 rows. 2. E. acanthostoma 



3. Evasterias troschelii (Stimpson) Verrill. 



Asterias troschelii Stimpson; Asterias branchiata Perrier; Asterias 

 (Diplasterias) epichlora De Loriol. 



Rays 5. Dorsal spines numerous, unequal, arranged net-like or areo- 

 late or clustered; larger spines capitate or truncated, smaller ones acute or 

 club-like; marginals in regular rows, longer than dorsals; interactinals 

 still longer, forming 4 to 6 regular close rows, spines curving upward; 

 mouth spines elongated ; pedicellariae numerous. — Numerous, in deep water 

 and along shore. 



la. Evasterias troschelii rudis Verrill. 



Size large ; dorsal spines not clustered ; spines medium or small, numer- 

 ous, not grouped, mostly club-like, capitate or rather sharp, arranged in 

 an open net-work with large papular areas; papulae numerous; inter- 

 actinal spines crowded. — Numerous, in deep water and along shore. 



lb. Evasterias troschelii densa Verrill. 



True to type in form. Dorsal spines somewhat capitate, nearly uni- 

 form in size, forming a close net-work, in single lines or somewhat irregular 

 but not clustered. — Not numerous, along tide line. 



