412 
THE VOYAGE OF H.M.S. CHALLENGER. 
value of the cortex for purposes of classification is very trifiing, in the same family 
some sponges may possess it and others not. The spherasters seem at first sight more 
suggestive of a Tetractinellid origin, but very slight inquiry is necessary to show that 
these spicules are not specially characteristic of the Tetractinellida, indeed on the whole 
they would appear to be more widely distributed among the Monaxonids. The only 
Tetractinellid sponge in which they appear with the same characters as in Tethya is 
Aurora, with its two species, Aurora glohostellata and Aurora reticulata; in the 
Monaxonids, on the other hand, similar forms of aster are not confined to Tethya, e.g., 
they occur in the new species Dori'pleres dendyi, a sponge which possesses neither a 
cortex nor a radiate arrangement of the megascleres, and in the widely different species 
Dictyocylindrus stuposus, Bowerbank, one of the Axinellidse. Again, the transition 
from an aster without a distinct centrum to one in which the centrum is well developed 
is so easy, and the transition is so frequently met with, that the spheraster, as distinct 
from asters with small centrums, is not of much value in classification, it is scarcely of 
generic value even. Contrary to the opinion of some spongologists, asters are so 
commonly present among the Monaxonids that the material out of which the spheraster 
might arise may readily be found within that group. Take the Axinellidae for example ; 
here we have as aster-bearing sponges: — Raspailia stelligera, 0. Schmidt^; Dictyo- 
cylindrus fasicularis, Bowerbank^; Dictyocylindrus stuposus, Bowerbank^; Hyme- 
desmia stellivarians. Carter ^ ; Hymeniacidon moorei, Carter,® both these last two 
species with oxyasters ; Hymeniacidon spinatostellifera. Carter ® ; Hymeniacidon 
capitatostellifera. Carter,^ characterised by a remarkable form of spheraster ; Hymenia- 
cidon trigonostellata. Carter,® in which the aster is a curious microcalthrops with 
terminally spined actines, reminding one of a tetralophous microcalthrops ; Axos jia- 
helliformis. Carter®; Axos cliftoni (Gray)^®; Hymedesmia stellata, Bowerbank,^^ with 
a chiaster. In Monaxonids other than Axinellids we have Sclerochalina asterigena, 
0. Schmidt,^^ though it is possible that the asters which Schmidt figures in connection 
with this may not be proper to the sponge; Chondrilla sacciformis, Carter^®; Suherites 
1 Spong. Atlant. Gebiet., p. 60, pi. v. fig. 14. 
^ Mon. Brit. Spong., vol. ii. p. 110 ; vol. iii. p. 45, pi. xviii. 
® Op. cit., vol. ii. p. 116 ; vol. iii. p. 47, pi. xix. figs. 1-7. 
* Ann. and Mag. Nat. Hist, ser. 5, vol. vi. p. 50, pi. iv. figs. lOct-e. 
^ Loc. cit, p. 50, pi. iv. figs, llo-c. 
® Loc. cit, p. 51, pi. iv. figs. \Zor-d. 
^ Loc. cit., p. 51, pi. iv. figs. 12a-c. 
® Loc. cit, p. 52, pi. iv. figs. 14a-rf. 
® Op. cit, ser. 5, vol. iii. p. 285, pi. xxvi. figs. 1-4, 1879. 
Bowerbank, Mon. Brit. Spong., vol. i. pi. x. fig. 197 ; Gray, Proc. Zool. Soc. Lend., p. 546, 1867 ; and Bowerbank, 
Proc. Zool. Soc. Lond., p. 321, pi. xxix., 1873 ; Carter, Ann. and Mag. Nat. Hist, ser. 5, vol. iii. p. 285, pi. xxvi. figs. 5, 
6 , GOr-C. 
Mon. Brit. Spong., vol. ii. p. 146 ; vol. iii. p. 71, pi. xxviii. figs. 5-8. 
Spong. Kiiste von .Algier, p. 8, pi. ii. fig. 5. 
Ann. and Mag. Nat Hist., ser. 5, vol. iii. p. 299, pi. xxvi. figs. 9, 11, 12. 
