WEST INDIAN STARFISHES 149 



Genus Luidiaster Studer, 



Luidiaster Studer, Sitzungs. Naturf. Freunde, Berlin, xvi, pp. 130, 131, 



1883; Anhang Abhandl. K. Preuss. Akad. Wiss., Berlin, pp. 49, 51, 1884. 



Ludwig, Notomyota, 1910, p. 451. Fisher, op. cit., 1911?>, p. 127. 



VerrUl, op. cit. p. 311, 1914. 

 Acantharchaster Verrill, Proe. U. S. Nat. Mus., xvii, p. 268, 1894. (Type, 



A. dawsoni Ver.) 



Rays usually five, angular, tapered. Disk small. Interradial 

 aetinal plates few, confined to the disk, spinous and with pec- 

 tinate pedicellarias. 



The dorsal surface is covered with small, unequal, thin plates, 

 mostly in the form of protopaxillje and spinose parapaxillae.^ 

 The latter have a low, round column and bear a large, central, 

 articulated spine surrounded at base by a circle of small spin- 

 ules; they are found on the disk and usually along the median 

 part of the rays. The protopaxillse are smaller, and part of 

 them bear only small spinules ; others have a small central spine. 

 The papulse occur, in the adults, on most of the disk and entire 

 basal part of the rays. Marginal plates of moderate size, more 

 or less alternate, spiniferous; those of the upper series smaller 

 than those of the lower, rounded, with a central eminence bear- 

 ing a large, movable spine, sometimes with a group of small 

 spinules around its base. The plates of the lower series may 

 bear one or two large spines surrounded by spinules. There are 

 no odd interradial marginal plates. 



Large double-pectinate pedicellarise are normally present on 

 the interactinal plates or over their sutures in the adults, but 

 may be partly or wholly lacking in the young. Similar pedi- 

 cellarias of smaller size and fewer valves may occur on the mar- 

 ginal and dorsal plates; rarely on the adambulacral plates. 



The larger interactinal compound pedicellarias may have ten 

 to twelve or more incurved papillae on each side, while those 

 of the dorsal surface have usually three to six. The central dor- 

 sal pore is very evident and is surrounded by papillaB. The 

 adambulacral plates have a salient inner angle, and bear a hor- 

 izontal divergent group of slender furrow-spines and a trans- 

 verse aetinal row of long spines, two, three, or more ; rarely one. 



1- See pages 84, 85, above, for these terms. 



