In a paper on dolomitization of siliceous microfossils by B. K. Holdsworth (for reference, see this Bibliography Vol. 31, No. 8, 14 E67-07193) the sponge Hyalostelia is referred to the Heteractinellida, described as 'an exclusively siliceous group.' It is here pointed out that Hyalostelia belongs to the Hexactinellida, not the Heteractinellida and that the nature of heteractinellid spicules is actually not known. There is evidence that they may be calcareous.