WEST INDIAN STARFISHES 153 



vex, encroaching more or less on the upper side of the disk and 

 rays. They are often entirely granulose, sometimes spinulose, 

 and often have one or two superior spines or tubercles. Infero- 

 marginals spinulose and spinose, prolonged actinally, most of 

 them reaching the adambulacral plates, but one or two inter- 

 radial pairs may not reach the adambulacral plates, and in that 

 case one or two pairs of small adoral interactinal ossicles may in- 

 tervene, but these do not form regular rows, nor an important 

 triangular area.* 



The inferomarginals bear marginal spines and are closely 

 spinulose and fasciolated laterally. Adambulacral plates are 

 equal in number to the inferomarginals; the inner end is angu- 

 lar. They have a longitudinal group of about three, rarely four, 

 furrow-spines, and two transverse rows, or a divergent group, on 

 the actinal side, often with the central or aboral spine enlarged. 

 The papulae stand singly around the dorsal paxillas; they are 

 generally absent along the median line. Dorsal pore often in- 

 distinct or lacking ; sometimes present. Superambulacral plates 

 are well developed. Pedicellarias are generally lacking; some- 

 times they are present on the adambulacral plates, and then are 

 papilliform, with two, three or more valves. They sometimes 

 occur also on the dorsal paxilla and on the superomarginal plates. 



The madreporic plate is commonly concealed by the dorsal 

 paxillffi; in some species it is exposed. 



Species of Astropecten are very numerous and have been 

 found in all tropical and w^arm-temperate seas in suitable locali- 

 ties. They live mostly on sandy or muddy bottoms, in rather 

 sheltered localities, when in very shallow water, but on the open 

 sea bottoms when in water deep enough to be beyond the active 

 action of the waves. 



They customarily live buried just beneath the surface of the 

 sand, keeping up a free communication with the water for respir- 

 ation by means of currents drawn through the fasciolated grooves 

 by ciliary action. But they can also live exposed, and can glide 

 along quite rapidly by means of their large, muscular, ambulacral 

 feet. 



They are most numerous in depths of 10 to 60 fathoms, but 



* Certain species having a notable group of interactinal plates were made 

 a separate genus, Astropectinides, by me (1914a, p. 321). 



