312 VERRILL 



eminence bearing a single large, movable spine, with a group of 

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

 bear two or more similar large spines surrounded by spinules. The 

 upper marginal plates form a narrow margin along the rays. 



The dorsal surface is covered with small, unequal plates in the 

 form of protopaxillae and spinose parapaxillae. 1 The latter have a low, 

 round column and bear a large, central, articulated spine surrounded 

 at base by a circle of small spinules ; they are found on the disk and 

 along the median part of the rays. The protopaxillae are smaller, and 

 part of them bear only small spinules; others have a small central 

 spine. The papulae occur on most of the disk and the entire basal 

 part of the rays. 



Peculiar double pectinate and fascicled pedicellariae exist on the 

 dorsal surface of the rays and disk, and a single one, of larger size, 

 occupies the center of each actinal interradial area (see pi. xxxiv, 

 P, P) ; in one case a similar structure replaces the two upper mar- 

 ginal plates in the interradial angle. These large actinal compound 

 pedicellariae may have ten to twelve incurved papillae on each side, 

 while those of the dorsal surface have usually three to six. Some of 

 the latter have three convergent groups of curved papillae. The 

 central, dorsal nephridial pore is very evident and is surrounded 

 by papillae. The adambulacral plates have a salient inner angle, and 

 bear a horizontal divergent group of furrow-spines and a transverse 

 actinal row of long spines. The jaw-plates are large and bear simple 

 marginal and actinal series of long spines. 



LUIDIASTER DAWSONI (Verrill) Ludwig. 

 Plate xxxm ; plate xxxiv; plate xxxv, figure 2 (type). 



Archaster dawsoni VERRILL, in Whiteaves, Report of Progress of Geological 



Survey of Canada, for 1878-79, p. 194^ [p. 5], 1880. 

 Acantharchaster dawsoni VERRILL, Proc. U. S. Nat Mus., xvn, p. 269, 1894. 



Fisher, 1910, p. 549. 

 Luidiaster dawsoni LUDWIG, 1910, p. 452. Fisher, 191 ib, p. 128, pi. xxv, 



fig. 2; pi. xxvi, fig. 3; pi. xxvii, fig. 2; pi. LV, figs. 3, 30; pi. LVI, fig. 5; pi. 



cxix, fig. 2; pi. cxx. 



Rays five, long, acute. Radius of the disk, 17 mm.; of rays, 

 100 mm. ; ratio, 1 : 6, nearly. The rays are long, flat, regularly 

 tapered. The upper surface is loosely covered with small ossicles 

 (protopaxillae), those toward the margins of the rays bearing only 

 circular groups of very minute short spinules ; but along the middle 



1 See pages 280, 281, for explanations of these terms. 



