( 109 ) 
a quantity of spined a-spiraxons. Evidently such spined a-spiraxons 
will exhibit the twisted nature the less distinctly the more the 
spines are developed. It is, therefore, not practical in this case to 
make distinctions, based on the number of revolutions. Especially not 
because there exists a great diversity with many transitions. I prefer, 
therefore, to propose for spined @-spiraxons the general term spini- 
spirae, to which I bring the spicula called by previous authors spira- 
sters, metasters, plesiasters, and also (partly) spinispirules, sanidasters ete. 
Sorras (1888 p. LXIIT) has given the following definition of the 
spiraster: “a spire of one or more turns, produced on the outer side 
into several spines.” Scnurze & LENDENFELD (1889 p. 28) say that it 
is a leicht gewundener gestreekter Aster mit dickem, dornenbesetztem 
Schaft”, a definition which LENDENFELD (1890 p. 426) modified into: 
„ein kurzer und meist dicker, leicht spiralig gewundener Stab mit 
starken, meist dieken und kurzen, kegelförmigen Dornen”. Sorras 
distinguished #metasters” and #plesiasters” from his spirasters, but 
he acknowledges himself that: “the three forms present a perfect 
eradational series, so that it is frequently difficult when they all occur 
associated in the same sponge, to distinguish in every case one variety 
from the other’. Now it happens very frequently indeed that they 
all oeeur associated in the same sponge and that all gradations are 
met with. One only needs to read Sorras’ own descriptions and to 
compare them with his illustrations, e.g, of the many “species” of 
Thenea, Poecillastra, Sphinctrella i.a. in order to become convinced 
that it is practically impossible to distinguish spirasters, metasters and 
plesiasters. ScHurze & LeNDENrELD, therefore, did not adopt the latter 
two terms. 
I am of opinion that the name spinispira can be likewise applied 
to the spicula which Sorras calls amphiaster; at any rate to such 
amphiasters as are said to occur in Stryphnus niger Sou.) A great 
confusion exists, with regard to the word amphiaster. The name 
is first used by Ripuuy & Denny (1887 pp. XXI and 264), who 
say that the amphiaster is composed of „a cylindrical shaft bearing 
a single toothed whorl at each end; occurring for example, in 
Awoniderma mirabile...’? The authors give an illustration by fig. 9 on 
their Pl. XXI, and a further explication saying: “amphiastra = biro- 
tulates (Bowerbank); amphidisks (auctorum).” But SoLnas says (1888 
p. LXIV) of Ais amphiaster “the actines form a whorl at each extremity 
of the axis, which is straight”; herewith a woodcut on p. LXI. 
bi] 
1) In his preliminary account on the Challenger-Tetractinellids (1886 p. 193) 
Soutas calls this spiculum “amphiastrella”, 
5 
Proceedings Royal Acad. Amsterdam, Vol, V, 
