492 THE VOYAGE OF H.MS. CHALLENGER. 
in his later work’ the independence of the genus is recognised, and two new species 
dredged during the “Talisman” Expedition have been referred by him to Hymenaster 
and “named,” but their descriptions have not yet been published. 
The dredgings of the Challenger Expedition have now shown that Hymenaster 
possesses a world-wide distribution in deep waters, and that the genus exhibits a 
remarkable amount of morphological plasticity, no less than twenty-four species being 
now known. 
The bathymetrical range of the genus is also remarkable, as, with the exception of the 
type form (Hymenaster pellucidus), which ranges from 70 to 1539 fathoms (fide 
Danielssen and Koren), all the species are confined to the Abyssal zone. One, Hymenaster 
mfernalis, extends to 2900 fathoms, the greatest depth at which starfishes have hitherto 
been found ; and four other species occur in depths greater than 2000 fathoms. 
The character of the adambulacral armature, which does not form transverse combs of 
webbed spines, and the structure of the actinal skeleton, composed of greatly developed 
actino-lateral spines, overlaid with a membranous tissue, forming the whole actinal 
floor of the test, constitute differences which, in my opinion, emphatically separate 
Hymenaster generically from Pteraster; and its divergence from the other members of 
the family Pterasteridz is equally well marked. 
The general facies of the type appears to be one of great antiquity. This, however, 
is not the place to discuss, as I should desire, the archaic relationships of existing 
Asterids; and I would therefore now only briefly direct attention to the remarkable 
resemblance and, in many respects, apparent similarity of general character, which exist 
between Hymenaster and the recently described Loriolaster of Stiirtz® from the Lower 
Devonian slates of Bundenbach. 
Chorology of the Genus Hymenaster. 
a, Geographical distribution :— 
ATLANTIC: Seven species between the parallels of 81° N. and 40° S. 
Hymenaster pellucidus, from the Faerée Channel, off the coast 
of Norway, and the islands of Jan Mayen and Spitzbergen. *Hymen- 
aster nembranaceus, south-west of Cape Finisterre. Hymenaster 
rex and Hymenaster giboryi, dredged by the “ Talisman” Expedition. 
*Hymenaster anomalus, north of the Island of Tristan da Cunha. 
Hymenaster modestus, off the coast of the United States of North 
America. *Hymenaster pergamentaceus, off the coast of South 
America, east of Buenos Ayres. 
' Ann, Sci. Nat. (Zool.), 1885, 6e Série, vol. xix. Art. No. 8, p. 69. 
? Paleontographica, 1886, Bd. xxxii. p. 94, Taf. xii., xiii. 
