REPORT ON THE ASTEROIDEA. 83 
II. Madreporiform body simple, exposed, Adambuiacral armature all spiniform, in co- 
ordinated groups, subastropectenoid. Adambulacral plates broad. (Zethyaster.) 
A. Rays long. Marginal plates seventy to eighty in the adult. : , ; subinermis. 
B. Rays short. Marginal plates twenty to thirty in the adult. : ; ; parelit. 
Chorology of the Genus Plutonaster. 
¢ 
a, Geographical distribution :— 
Artantic: Five species between the parallels of 75° N. and 10° 8. 
Plutonaster rigidus and Plutonaster rigidus, var. senuarmata, off 
the east coast of the United States of America. Plutonaster abbre- 
viatus and Plutonaster notatus, in the neighbourhood of the Azores. 
Plutonaster bifrons in the Faerde Channel, off the coast of Portugal, 
and off the coast of North America (the latter occurrence on the 
evidence of a single immature specimen, which might belong to a 
variety). This species has also been obtained ( fide Norman’) in the 
Barents Sea between Spitzbergen and Nova Zembla, in lat. 73° 41’ 
12” N., long. 22° 58’ 30” E., at a depth of 210 fathoms. The 
examples are stated to be young. Plutonaster marginatus in the 
South Atlantic, near the Island of Ascension. 
Pactric: One species between the parallels of 30° and 40° S. 
Plutonaster ambiguus, off the east coast of Australia, near 
Sydney. 
8. Bathymetrical range : 210 fathoms to 1360 or 1700? fathoms. 
All the species except Plutonaster marginatus belong exclusively to the 
abyssal zone. Of the remaining five, two only, Plutonaster bifrons and Pluto- 
naster ambiguus, have been found in depths less than 1000 fathoms. 
Greatest range of one species : Plutonaster bifrons, 210 to 1360 fathoms. 
y. Nature of the Sea-bottom: Two species, Plutonaster rigidus and Plutonaster 
bifrons, are found on the Blue mud, and Plutonaster bifrons is also found on 
Globigerina ooze. Plutonaster ambiguus is found on Green mud. Plutonaster 
notatus is found on Pteropod ooze; the nearly allied Plutonaster abbreviatus 
on Voleanic mud. Plutonaster marginatus on Volcanic sand. 
1 In W. 8. M. D'Urban on the Zoology of Barents Sea, Ann. and Mag. Nat. Hist., ser. 5, vol. vi., 1880, 
p. 260. 
2 The uncertainty in the limit of greatest depth arises from not knowing at which of two stations Plutonaster 
rigidus was dredged. 
