Comprehensive DescriptionRead full entry
“Genus Perknaster, n. gen.
Disk large and more or less inflated. Rays cylindrical and tapering.
Abactinal and lateral surfaces up to the adambulacral plates covered with small undistinguishable plates, which bear groups of short, equal spinelets, covered with skin, dispersed in tufts or paxilliform groups, more or less compactly placed.
Armature of the adambulacral plates disposed in one or two transverse series; the innermost spinelet usually large and thickly skin-covered. No small inner spinelet placed high up in the furrow as in Cribrella.
Madreporiform body distinct, situated about midway between the centre of the disk and the margin; surface marked with fine, convoluted striations.
Anal aperture subcentral and inconspicuous.
Ambulacral tube-feet in regular biserial arrangement, and having large fleshy terminal disks.
No pedicellariae of any kind present.
Remarks.—This genus, though allied to Cribrella, is at once characterised by the large development of the disk, by the compact structure of the abactinal and lateral skeleton, by the homogeneity of the marginal plates, and by the character of the armature of the adambulacral plates. The general facies of the forms I have included in the genus is very different from that of Cribrella, or any other type.”
(Sladen, 1889: 550)