REPORT ON THE ASTEROIDEA. 121 
Infero-marginal plates extending on the actinal area. Supero-marginal plates crowded 
with numerous small, uniform, cylindrical, miliary spinelets ; no large prominent spines. 
Infero-marginal plates covered with large, flat, squamiform, adpressed spinelets, with one 
or more similar, large but short, flattened spinelets at the margin adjacent to the supero- 
marginal plates. 
Abactinal area with subhexagonal oblong imbricating plates, bearing paxilliform 
groups of short spines. A conspicuous medio-radial series larger than the rest. The 
other plates form regular obliquely transverse series, each plate imbricating on the next 
in its own series by a single prolongation of peculiar form developed from the inferior 
surface of the plate. Papule regularly distributed. 
Actinal interradial areas almost nil, with very few actinal intermediate plates. 
Armature of the adambulacral plates triserial, simulating that of Astropecten. A 
series of three geniculated pointed spines in triangle on the furrow margin ; followed by 
one or two outer series of two to four flattened spines. 
Madreporiform body in mid area. Occasional pedicellarise (subforficiform) are present 
in the median series of spines on the actinal surface of the adambulacral plates. 
Remarks.—The genus Archaster, as originally constituted, comprised the two species 
named by its founders Archaster typicus and Archaster hesperus ; both are very remarkable 
forms and are widely separated from one another structurally. Indeed it is impossible any 
longer to retain them in the same genus; and it is difficult to account for their long 
companionship except on the ground that Archaster hesperus is of rare occurrence and 
has seldom been brought to Europe, and that nearly all the specimens preserved in 
museums are dry and more or less damaged. The only point then to determine is as to 
which of the two forms should stand as the type of the genus Archaster, which, in other 
words, would have been so regarded by its founders, and which of the two represents best 
the characters mentioned in their brief and very general diagnosis of the genus. That 
Archaster typicus fulfils these conditions I think there can be but little doubt; in the first 
place there is the specific or trivial name; 2d, its priority in the order of description ; 3d, 
its close conformity with the generic diagnosis, which would be very insufficient for a well- 
preserved example of Archaster hesperus; 4th, I am extremely doubtful whether any anus 
is present in Archaster hesperus, and the presence of this aperture was in Miller and 
Troschel’s opinion ‘the most marked character of all. On these grounds I consider 
Archaster typicus as the type form of the genus Archaster; whilst Archaster hesperus 
constitutes the type of a genus for which I propose the name of Craspidaster, the 
characters of which will be discussed on a subsequent page. 
Of all the species which have been referred to the genus Archaster since 1840 one 
only—Archaster angulatus of Miller and Troschel—presents the same structural characters 
as the type; the other forms have now been distributed amongst several different 
genera. 
(ZOOL, CHALL, EXP.—PART LI.—1887.) 16 
