1028 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
ginal, or about one-half the length of ray. A third series extends to the seventh, or one-fifth lergth 
of ray. Between first and seventh plates the longitudinal series multiply rapidly. Regarding the 
plates in series extending interradially, those opposite mouth plates and first 2 adambulacrals are 
irregular. Actinal surface of the plates convex, not raised into an abrupt and prominent keel as in 
some species of the genus; the convexity is most marked near the inferomarginals. Plates bear a 
crown of uniform, blunt, papilliform spinelets, often flower-like in appearance. On rays these spine- 
lets tend to become slenderer. Very shallow grooves are present between the plates, roofed over by 
spinelets. 
Madreporic body is very large (7 mm. in diameter) and is situated slightly nearer the margin than 
midway between it and center of disk. It is concealed by large paxillse, there being actually on its 
surface about 18, one of which is much larger than the rest. Outline of madreporic body is subcir- 
cular, but the rim is irregularly scalloped. 
Color in alcohol bleached brownish or yellowish. Color in life probably deep yellow, but was not 
recorded. 
Young: The smallest specimen of this species (R =18 mm., r = 7.5 mm.) differs somewhat from 
the adult, chiefly in having relatively shorter rays (superomarginals 18) and less prominent infero- 
marginals. These do not extend conspicuously beyond the superior series, the latter being more 
arched than in the adult. The inferomarginal spinules are not yet developed, the plate being crowded 
with rather minute, papilliform, sharp spinelets. Paxillse have the adult character, but are much 
smaller. Inferomarginal spinules have appeared in one specimen with R = 34 mm. 
Anatomical notes: In this species the gonads extend out into the ray, and are arranged in a longi- 
tudinal series on either side of the median radial area, depending from their respective rachides like a 
row of digitate glands. The largest of the genital tufts is near the interradial line, and they gradually 
decrease in size distad, the series ending just beyond the middle of the arm (see text figure). This j 
arrangement of the gonads also obtains in D. eximius Fisher, a very distinct species from California, 
and although not mentioned by the describer, I believe it will also be found to hold true for Dipsacaster 
sladeni and D. pentagonalis Alcock. Possibly the group to which siadeni, the present species, and that 
from California belong may be subgenerically different from pentagonalis. .1 udging from the figures, . 
the adambulacral armature of the last species is considerably different from the present species. 
The anal aperture opens directly from a single sac-like intestinal coecum, which lies in the interra- 
dius to the left of that occupied by the madreporic body. This sac, the total length of which is 2 
about two-thirds the minor radius, has a single small pocket-like branch at one side. A short 
intestine joins the larger sac with the dorsal stomach. The aperture of the intestine into the sac is 
very nearly beneath the anus, but is separated from the latter by a broad fold of the wall. Mr. Alcock, 
in describing Dipsacaster sladeni (Ann. N. H., ser. 6, vol. xi, p. 87, pi. v), states that the anal pore is 
not in connection with the intestine, and includes this as a character of the genus. Inasmuch as the 
present species is very closely related to sladeni, and consequently undoubtedly a Dipsacaster, that 
character can not be regarded as of generic importance. 
Superambulacral plates are feebly developed, and do not extend far along the ray. They are 
apparently absent from the first few ambulacral plates. 
Localities: Type (no. 21151, U. S. National Museum) from station 3916, south coast of Oahu 
Island, 299-330 fms., gray sand and mud; bottom temp., 44°. Taken also at the following stations, 
in all, 13 specimens: 
Record of localities. 
Station. 
Locality. 
Depth. 
Nature of bottom. 
3866 
Northeast approach to Pailolo Channel, between Maui and 
Molokai islands. 
do 
Fathoms. 
283- 284 
284- 290 
284-290 
304-308 
Gray mud, fine sand. 
Fine sand, mud. 
Globigerina mud. 
Fine white sand and mud. 
Fine gray sand and mud. 
do 
8Q08 
South coast of Oahu Island 
sqm 
do 
This species is most nearly related to Dipsacaster sladeni Alcock. It differs in the marginal plates, 
which do not correspond on the outer third of the ray, but alternate; in the armature of the infero- 
