536 THE VOYAGE OF H.M.S. CHALLENGER. 
Synopsis of the Genera included in the Family EcHINASTERIDS. 
A. Disk large. Rays numerous, Armed with large isolated spines covered 
with membrane beset with calcareous granules. Numerous madre- 
poriform bodies. orficiform pedicellarie present . . : 
a. A single genus c 2 . : : . . é 
B. Disk small. Rays usually ave Armed with large spines beset with scales 
or asperities. One madreporiform body. No pedicellariw present. 
No interbrachial partitions . . : . . . . 5 
a. A single genus : . : . : - 
C. Disk small or medium-sized. Beye five or six. Spinulation small: spinelets 
isolate or grouped. No pedicellarie present . . . 
a. Armature of the adambulacral plates simple or disposed in Eoancane 
series. 
a. Abactinal plates bearing small spinelets, in more or less com- 
pact groups. 
a, Disk small. Marginal plates usually distinguishable. 
Adambulacral plates with a small inner spinelet 
placed high in the furrow : 
8. Disk comparatively large. Marginal plates crpentically 
undistinguishable. No small inner spinelet on the 
adambulacral plates. - : : : “ 
b. Abactinal plates bearing simple isolated spines 
b. Armature of the adambulacral plates disposed in a double jong util 
series. Abactinal plates forming a wide-meshed network 
and bearing compact groups of spinelets. . 
D. Disk moderately developed. Rays five. Abactinal plates pany ae 
posed, bearing small isolated spinelets, Marginal plates with large 
valvate pedicellariz. Actinal intermediate plates bearing one or 
more large flattened spinelets 
a. A single genus 5 : . . . 
Subfamily AcANTHASTERIN#, Sladen, 1888. 
Genus Acanthaster, Gervais. 
ACANTHASTERINZ. 
. Acanthaster. 
MITHRODIINE. 
. . Mithrodia. 
EcHINASTERIN. 
. Cribrella. 
. Perknaster. 
. Lchinaster. 
4 . Plectaster. 
‘VALVASTERINE. 
Valvaster. 
Stellonia (pars), Agassiz, Mém. Soc. Sci. Nat. Neuchatel, 1835, t. i. p. 191. 
Echinaster, Gray, Ann. and Mag. Nat. Hist., 1840, vol. vi. p. 281. 
Acanthaster, Gervais, Dict. Sci. Nat., suppl., 1841, t. i. p. 474. 
Echinites, Miiller and Troschel, Archiv f. Naturgesch., 1844, Jahrg. x., Bd. i. p. 180. 
Acanthaster is a very isolated type, having a facies altogether unlike that of any other 
form. ‘The genus is confined to tropical waters, and, though ranging over a wide area of 
distribution, the amount of morphological plasticity exhibited is very slight. 
uncertainty as to whether the form from Mauritius, so carefully described by de Loriol,’ 
can really be recognised as a species independent from Acanthaster echinites; and I am 
equally doubtful as to the validity of the claims of Acanthaster ellisii. 
1 Mém. Soc. Phys. et Hist. Nat. Genéve, 1885, t. xxix., No. 4, p. 6. 
I feel some 
