1046 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
ee. Abactinal plates covere'd with flat granules of considerable size, and irregular, often gro- 
tesque shapes. Numerous large bivalved pedicellariae on both surfaces, but not on 
marginal plates. Marginal and actinal plates covered with polygonal or irregular 
granules Gilbert aster 
dd. Marginal plates with rigid tubercular spines, or tubercles. 
e. Distalmost 2 or 3 superomarginal plates in contact medially. Abactinal plates smooth, 
having a central tubercle on the radial series Calliaster 
ee. Marginal plates separated throughout the ray. Abactinal, marginal, and actinal plates 
bearing conical spines surrounded by granules sheathed in a thick, pulpy, investment. 
Evoplosoma 
cc. Form stellate; many of the distal superomarginal plates in contact medially. Rays slender, 
at least in outer part; disk well developed. 
d. Abactinal plates smooth, bordered by small, oblong, roundish, or quadrate granules. 
Actinal plates bearing a few central, tubercular granules, and bordered by bead-like 
granules. Inferomarginal plates without spines Astroceramus 
dd. Abactinal plates granuliferous, bearing erect sharp spines on radial areas. Infero- 
marginal and actinal intermediate plates bear prominent, mobile, sharp, appressed 
spines Calliderma 
aa. The whole test covered by a membrane or skin obscuring the outlines and surface of the plates. 
b. Papulae single, medium-sized, not in areas. Abactinal membrane smooth. All granules of test' 
are beneath the membrane. Plates polygonal or roundish, close-fitting. Pedicellarise 
elevated, spatulate, pincer-shaped Antheniaster 
bb. Papulae very small; in areas. Integument or skin closely beset with small superficial granules. 
Plates strongly stellate. Pedicellarise small, low, slit-like, as in Pentaceros. . .Goniodiscides 
Subfamily MEDIASTERINU Verrill, 1899. 
Mediasterinse Verrill, Revision of Certain Genera and Species of Starfishes, with Description of New Forms. <Trans. 
Conn. Acad., vol. x, Aug. 1899, p. 177. 
Genus MEDIASTER Stimpson. 
Mediaster Stimpson, Joum. Bost. Soc. Nat. Hist.’, vol. vi, 1857, p. 490, pi. 23, figs. 7-11. Type Mediaster xqualis Stimpson. 
Isaster Verrill, Proc. U. S. Nat. Museum, vol. xvn, 1894, p. 257. Type Archaster bairdii Verrill. 
The following species of Mediaster differs from M. xqualis, the type of the genus, in several important 
respects. The internal connecting ossicles a of the abactinal plates are absent from a very definite 
triangular interradial area, the roundish or somewhat irregular plates being there in close contact, and 
the papulae consequently absent. In Mediaster xqualis, however, both the papular pores and the radi- 
ating connecting ossicles are present right up to the interradial septum, there being only a narrow 
area, where the septum attaches to the abactinal integument, free from papulae and ossicles. The 
appearance, when prepared specimens of the two forms are viewed from the internal side, is quite differ- 
ent. In Mediaster ornatus the pedicellariae are more pincer-like, especially on the actinal surface, 
instead of being low as is the case with xqualis. In the Hawaiian species the granules of the abactinal 
paxillae are more delicate, ornate, and are not so closely crowded on top of the tabulum as in xqualis. 
In ornatus the furrow spines are 6 or 7 in number, delicate and compressed, and disposed in very 
regular combs. In xqualis they are 3 to 5, stout, unequal, subprismatic, not different in thickness from 
the 2 actinal series. 
Mediaster ornatus, new species. 
PI. xvi, figs. 3, 3a-b; pi. xx,figs. 1, 2. 
Rays 5. R=52 mm.; r=21.5 mm.; R=2.42 r. Breadth of rays at base, 21 mm. 
Regularly stellate, with a broad disk, usually inflated over radial areas, and with symmetrical, 
regularly tapering rays, which have a broad. base. Rays bluntly pointed. Interbrachial arcs wide and 
rounded. Sides of body well rounded, actinal surface plane. 
Abactinal paxillar area covered with medium-sized, ornate, tabulate paxillae, arranged in regular 
series parallel with the median radial. Paxillae of radial regions and center of disk are more widely 
a Ludwig (Mem. Mus. Comp. Zool., vol. xxxir, 1905, p. 126) has described Mediaster elegans (west of Cocos Island), in 
which there are no internal connecting ossicles. 
