Mr. H. J. Carter on Holasterella and Hemiasterella. 141 XIV. — On Holasterella, a Fossil Sponge of the Carboniferous Era, and on Hemiasterella, a new Genus of Recent Sponges. By H. J. Carter, F.R.S. &c. [Plate XXI.] In my description of Mr. James Thomson's fossil sponges from the Carboniferous Limestone of the South-west of Scot-land (' Annals,' 1878, vol. i. p. 133), I have stated that Dr. Millar had brought to my notice a stelliform spicule, " like a double star back to back," which is described and illustrated (pi. ix. fig. 11 &c). It is also stated (p. 134 ib.) that the three different spicules mentioned and figured " appear " to have belonged to " three different sarcohexactinellids respec-tively," of which the first (viz. fig. 8 &c.) had only been identified with the Hexactinellida or sexradiate-spicule sponges. If, however, a six-rayed form only is to be considered indica-tive of a hexactinellid sponge, then the two other stelliform spicules, which have respectively many more rays, must be considered indications of the existence of sponges which did not belong to the hexactinellid order. And this is now evi-dently the case ; for the fossil sponge about to be described will be found to have been exclusively composed of the many-rayed spicule (fig. 11, op. et loc. cit.). This interesting species, which has lately been discovered, and was forwarded to me in four pieces by Mr. James Thom-son of Glasgow, on the 2nd November last, I will now de-O 7 u 7 scribe, so far as the lapidification permits, under the name of Holasterella conferta, n. gen. et sp. (PI. XXI. figs. 1-8.) Fossil solid, massive, club-shaped, rising from a subcylin-drical base which, increasing gradually and subcylindrically upwards, terminates rather suddenly in an expanded, globular, lobate head (PI. XXI. fig. 1, a, b, c, d). Colour white. Com-position, opaque, translucent and transparent heavy spar (sul-phate of barytes), according to the position, with glistening aspect over the face of fracture and dull exterior. Surface even, irregularly undulating throughout ; presenting here and there more or less ovoid, sharp-margined depressions or pits of different sizes, which appear to have been the abodes of old and young crustaceans respectively (fig. l,f and fig. 2, a, a). Internal structure solid throughout, having been composed exclusively of stelliform spicules irregularly thrown together ; apparently faced by a layer of much smaller ones, arranged in some parts (which appear to be perfect, fig. 1, //, and fig. 2)
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