EASTERN TROPICAL PACIFIC ASTEROIDEA. 99 
. Key to the species of Pholidaster. 
Superomarginals and most of the disk-plates concealed by flat, skin-covered seales.......... squamatus. 
Superomarginals and primary disk-scales largely bare.................2200..-2000000-- distinctus. 
Myxoderma. 
Fisuer, 1905. Bull. U.S. Bur. Fish., 24, p. 316, as a subgenus of Zoroaster. 
Type-species: M. sacculatus FisHer, 1905. Loc. cit. 
This small group of sea-stars occurring off the coast of the western United 
States and Lower California in 284-916 fms. is well-cirecumscribed and Fisher 
has wisely (1919. Ann. Mag. Nat. Hist., ser. 9, 3, p. 392) raised it to full generic 
rank. In the same paper he has described a subspecies of each of the two com- 
ponent species but I doubt whether sufficient material has yet been secured to 
warrant recognition of subspecies. In any case, however, he has set forth so 
well the characters of these supposed subspecies in his key, that we need not dis- 
cuss them here. There are certainly two valid species. 
Key to the species of Myxoderma. 
Spines and spinelets more or less conspicuously sacculate; big pedicellariae in ambulacral furrow or on 
adambulacral spines; papulae in adults 3-5 in an area on base of rays abactinally. . . . sacculatum. 
Spines and spinelets little or not at all sacculate; no big pedicellariae in furrow or on adambulacral spines; 
papulae 1 or 2 in an area on base of rays abactinally.......................... platyacanthum. 
Bythiolophus. 
Fisuer, 1916. Proc. Biol. Soc. Wash., 29, p. 31, 1919. Bull. 100 U.S. N. M., p. 484, pl. 135, fig. 1—Ic, 
139, fig. 1, 2. 
Type-species: B. acanthinus Fisher, 1916. Loc. cit. 
This monotypic genus is based on a single sea-star taken by the ALBATROSS 
in Buton Strait, Celebes, in 559 fms. It is unquestionably a well-marked and 
noteworthy type. In the diagnosis as published in 1919, the presence of sub- 
ambulacral plates is mentioned; Dr. Fisher assures me this is a slip for super- 
ambulacral. In the key to genera of Zoroasteridae (1919, p. 471) Bythiolophus 
is said to have no adradial plates and in the figures 1 and le, pl. 135, as well as 
in the explanation of the plate, the series of plates adjoining the carinals on 
each side is called the superomarginal. But in the diagnosis of the genus (p. 484) 
and in the diagnosis and description of the species (p. 485) this series is consid- 
ered as adradial and the prominence of the adradial plates is emphasized. Dr. 
Fisher writes me that the key was prepared much later than the text and is 
