422 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.40. 



are added, until distally the plates have an even granular surface, 

 like that of actinal plates. Proximally most of the plates have a 

 large bivalved denticulate pedicellaria, the jaws much wider than 

 high. This occupies a third or a fourth the length of a plate. 



Mouth plates small, triangular with a fairly straight furrow mar- 

 gin, with nine or ten spinelets, the innermost heaviest. Surface 

 covered with spaced stout granuliform spinelets. 



Madreporic body small, near center of disk and about as large as 

 surrounding plates. Ridges radiating and coarse. 



Type-locality. — Station 5273, off western Luzon, 27 miles south- 

 west Corregidor Light; 114 fathoms; mud, shells, and coral sand. 



Type— Cat. No. 28657, U.S.N.M. 



Remarks. — This genus differs from Circeaster in lacking the abruptly 

 larger abactinal plates of rays, in having smooth marginals, and 

 regular tabulate radial plates; and from Lydiaster in the character 

 of abactinal, marginal, and adambulacral plates. Lydiaster is more 

 nearly related to Circeaster than to Pontioeeramus. Ceramaster is 

 distinguished by the wholly granulate tabulate abactinal plates and 

 Eugoniaster, which is perhaps the most nearly related form, has the 

 abactinal plates arranged without regularity although "tabulate," 

 and the adambulacral plates are of uniform width throughout. 



LITHOSOMA, new genus. 



Related to Iconaster Sladen, but differs hi having the regular longi- 

 tudinal radial series of abactinal plates completely surrounded by 

 granules, not on the lateral edges only, and in having the subam- 

 bulacral granulation short and spaced from the furrow comb, not 

 crowded and graduated into the furrow armature. All plates smooth 

 and bordered by a single series of granules, the plates of papular 

 areas sensibly elevated. Small spatulate excavate pedicellarise on 

 both surfaces. Disk large, rays long, slender, and beyond base of 

 ray composed only of marginal plates abactinally. 



Type. — Lithosoma actinometra, new species. 



LITHOSOMA ACTINOMETRA, new species. 



Rays 5 R = 155 mm., r = 42 mm., R = 3.7 r; breadth of ray at 

 base, 49 mm., at eighth superomarginal 19 mm. Disk large, rays 

 narrow; interbrachial arcs very open, the disk being arcuate pen- 

 tagonal and produced at the corners into the long slender rays, 

 composed abactinally of the marginal plates only. All plates smooth, 

 porcelain-like, bordered by a single complete series of granules flush 

 with the general surface; only the adambulacral and mouth plates 

 with granules on surface. Marginal places block-like massive, the 

 superomarginals, 40 in number, hi contact along median hue 

 beyond the seventh to ninth, and encroaching conspicuously upon 

 dorsal surface, being wider than high. Marginal granules small, 



