SHALLOW-WATER STARFISHES 57 



D. Interactinal ossicles numerous, stout, closely united in three to six longi- 



tudinal rows, usually bearing three to six or more close rows of 

 strong actinal spines. 



E. Dorsal spines arranged in a reticulate or areolate manner, or else grouped 



on the nodes ; but often forming a median row on the rays. Rays 

 normally five, stout. 



a. Dorsal spines stout, coarse, very unequal, capitate, acervate, forming con- 



spicuous angular reticulations with or without notable nodular 

 groups and often with median radial rows. 

 P. ochraceus (Brandt), p. 68. Calif, to Middle Alaska, 

 a'. Dorsal spines mostly in very prominent nodes or clusters ; reticulations less 

 conspicuous. 

 Var. nodiferus V., nov., p. 71. Calif, to Alaska, 

 aa. Dorsal spines small, or rather small, acute or obtuse, not strongly capitate, 

 usually forming evident reticulations. 



b. Dorsal spines exceedingly numerous, very small, obtuse or acute, forming 



conspicuous reticulations, with or without radial rows and a cen- 

 tral pentagon. Actinal spines stout, obtuse, but not strongly grooved 

 externally. 

 P. confertus (Stimp.), p. JZ- Calif, to Vancouver I. 



bb. Dorsal spines small, slender, not very numerous, forming an openly reticu- 

 lated pattern with a central pentagon and distinct median radial 

 rows. Actinal spines deeply gouge-shaped and often bifid. Disk 

 large. 

 P, Ussipinus (Stimp.), p. 76. Oregon. 



EE. Dorsal spines scattered, mostly without regular order, not reticulated, 

 but sometimes forming radial rows. Rays usually stout, five or six. 



d. Rays normally five. Dorsal spines large, with capitate or ovoid tips, not 



very numerous. 



e. Dorsal spines few, large, nearly equal, obtuse or strongly capitate and 



radially striate. Rays short. 

 P. capitatus (Stimp.), p. 81. S. California. 



ee. Dorsal spines more numerous, unequal, the tips ovoid or subconic and 

 striated, usually forming imperfect radial rows. Rays long, rounded. 

 Size large. 

 P. liitkenii (Stimp.), p. 83. S. Calif, to Vancouver I. Var. australis 

 Ver., p. 88. 



dd. Rays normally six ; dorsal spines very numerous, short, stout, conical, 

 acute or obtuse, striated, nearly uniformly scattered ; no evident ra- 

 dial rows. Interactinal spines in four to six rows. Disk large. 

 Size large. 

 P. giganteus (Stimp.), p. 89. 



DD. Interactinal ossicles fewer, usually forming only two rows, and mostly 

 bearing simple rows of spines. Dorsal ossicles openly reticulated. 

 Dorsal spines few. 



f. Rays normally five. 



g. Dorsal spines rather sparse, short, thick, subconic, striated, scattered or 



clustered, with distinct median radial rows. Actinal spines short, 

 obtuse, often flat, or slightly gouge-shaped at tip. 

 P. hrevispinus (Stimp.), p. 77. S. Calif, to Vancouver I. 



