1022 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
paxillar area, fewer spinelets to the paxillse, only 2 weak spinelets on the inferomarginal plates instead 
of the series of 3 of adult, no trace of an enlarged spinule on fhe superomarginals. The spinelets of the 
paxillse radiate, forming beautiful rosettes, and are not clustered in a bunch as is usual in large exam- 
ples. There are 3 to 5 of these spinelets, representing the marginal series of the adult, the central 
spinelets being absent. The teeth are much more prominent in little specimens. The transition 
between this and the adult is represented in the collection. The general facies of the adult is reached 
when the creature has attained a major radius of about 55 mm., at which age there are something over 
40 superomarginal plates. The immature specimens all have a low epiproctal hummock or cone, very 
pronounced in the little examples, but wholly absent in the fully adult forms. As mentioned in the 
previous paragraph, all the stages of the Oahu specimens have thicker rays than the typical form. 
Localities: Type (no. 21149, U. S. National Museum) from station 4095, northeast approach to 
Pailolo Channel, between Maui and Molokai islands, 290-286 fathoms, brown mud, fine sand, and 
globigerina; bottom temperature, 43.9° F. As detailed in the following table, the specimens were 
taken either from the northeast approach to Pailolo Channel (which separates Molokai from Maui) 
or in practically the same locality farther out, to the north of western Maui; or they were dredged 
off the southern coast of Oahu, most of the latter being not quite typical. The longitudinal distribu- 
tion of Psilaster attenuatus extends from 256 to 337 fathoms, the most favorable depth for large 
specimens being in the neighborhood of 290 fathoms. The nature of the bottom varies, specimens 
having been taken in globigerina ooze and mud, fine volcanic sand and rocks, gray mud and fine sand, 
sand and shells, fine gray sand, brown mud and fine sand with globigerina. 
Record of localities. 
Station. 
Locality. 
Depth. 
Nature of bottom. 
Fathoms. 
3865 
Northwest approach to Pailolo Channel, between Maui and 
Molokai islands. 
256-283 
Fine volcanic sand and rocks. 
3866 
do 
283-284 
Gray mud, fine sand. 
Fine sand, mud. 
do 
284-290 
3883 
do 
277-284 
Globigerina ooze. 
3884 
do 
284-290 
Globigerina mud. 
3908 
South coast of Oahu Island 
304-308 
Fine white sand and mud. 
3909 
do 
308-322 
Do. 
3910 
do 
311-337 
Fine gray sand , mud. 
3911 
do 
337-334 
Do. 
3916 
do 
299-330 
Do. 
3917 
do 
330-294 
Do. 
3918 
do 
294-257 
White sand, mud. 
4086 
North coast of Maui Island 
283-308 
Sand, shells. 
4087 
do 
308-306 
Fine gray sand. 
4088 
do 
306-297 
Do. 
4089 
do 
297-304 
Do. 
4090 
do 
304-308 
Do. 
4091 
do 
308-306 
Do. 
4095 
do 
290-286 
Brown mud, fine sand, globigerina. 
4096 
Northeast approach to Pailolo channel 
272-286 
Fine gray sand. 
In December, 1891, the Albatross made a few dredge hauls off the south coast of Oahu and 
secured about 60 specimens, the greater number of which are typical. They were taken at stations 
3470, 343 fathoms, white sand; 3471, 337 fathoms; 3474, 375 fathoms; 3475, 351 fathoms (four-fifths of 
the specimens) ; 3876, 298 fathoms. 
This species, of which about 230 specimens have been examined in all stages of growth, is one of 
the commoner forms of the medium depths. It is characterized by the long graceful rays, and by the 
form of its paxillse and the armature of marginal and adambulacral plates. It is most nearly related, 
among forms already described, to Psilaster acuminatus Sladen, which has been taken northwest of 
Port Hardy, New Zealand, and Simons Bay, Cape of Good Hope. It differs from Sladen’ s species 
principally in having longer and slenderer rays, in the covering of the marginal plates, and to a less 
extent in details of paxillse and adambulacral armature. The rays of attenuatus are even longer 
relatively than those of gracilis; gracilis, however, is widely different from attenuatus. 
