8 NATUEAL HISTORY BULLETIN 



It is proposed to include, at the end, a special list of the other 

 deep-water species (about 40) not reported upon, for the sake 

 of completeness. 



Thus the systematic part of this report will include about 82 

 species and subspecies, nearly all of which are redescribed in de- 

 tail, with their known distribution, etc. 



Comparatively few, even of the shallow-water species, have 

 ever been figured. Therefore some of them, though not new, 

 have been figured in this report. 



The drawings of structural details are by A. Hyatt Verrill, and 

 also most of the photographs. 



Class ASTERIOIDEA 



MORPHOLOGICAL FEATURES 



The Asterioidea ^ have a polygonal or star-shaped body, in 

 which the rays are direct prolongations of the body itself, and 

 contain extensions of the body-cavity and more or less of the 

 viscera, especially one or more pairs of gonads and a pair of di- 

 gestive glands ; generally, also, a lobe of the saccular stomach. 



The actinal or ventral side of the disk and rays has deep, 

 radial, ambulacral grooves, extending to the tips of the rays. The 

 roof of the groove is supported by two rows of ambulacral os- 

 sicles, arranged like rafters, or in close, inverted, V-shaped pairs 

 of plates or bars, between which are rows of pores for the pas- 

 sage of the tubular ambulacral feet or ' ' podia, ' ' which are usual- 

 ly terminated by a muscular sucker, but are pointed in the sub- 

 order Paxillosa. 



In the middle line of each ray and external to the ambulacral 

 plates are situated the radial nerve and blood-vessel ; and deeper 

 within, the median radial "water-tube" or ambulacral tube. 

 The radial water-tube supplies water to the podia through the 

 medium of muscular ampullae situated internally, above the 

 ambulacral plates. Usually there are two of these to each podium, 

 but in Echinaster, Ctenodiscus, and some other genera there is 

 only one. 



The grooves are bordered on each side by a row of plates 

 called adambulacral, which always bear spines. 



sThis spelling of the name is preferred because it is derived from As- 

 terias (not from Aster.) 



