SPONGES. -HALLMAiMN. 



J 19 



II.— DESCRIPTION OF THE GENERA AND SPECIES. 



Family SPIRASTRELLID.'E. 



Genus Spirastrella, Schmidt. 



Spirastrella montiformis, sp. nov. 



(Plate xxi., fig. 3, and fig. 21.) 



Sponge mound-shaped, rising to a central peak, on the 

 summit of which one or several oscida are situated; 

 upper aspect of sponge %mth short digitiform or ridge- 

 like processes on ivhich apical oscula are rarely to be 

 found. No rind. Spicides not aggregated into definite 

 fibres. Megascleres : — Tylostyli {sometimes reduced, to 

 styli), of varying length and stoutness, reaching a maxi- 

 mum size of "/lo X 12 f/. Microscleres : — Spirasters of 

 two kinds, viz., shorter tuberculated forms principally 

 confined to the superficial layer, 25 n long; and slender 

 zigzag sharp-spined forms cliiefly to be found in the 

 canal ivalls of the interior and reaching to 80 pi or more 

 in length. 



This species is represented in the collection by eight speci- 

 mens, all of which are preserved in the dry state. Although 

 showing a moderate amount of variability in external form, 

 they may be satisfactorily described in general terms as mas- 

 sive, sessile, somewhat mound-shaped sponges, roughly 

 circular in horizontal section, and usually prolonged upwards 

 into a more or less well-defined pinnacle. They are attached 

 by a broad base of only slightly lesser extent than the maxi- 

 mum transversal of the sponge, which is artained some short 

 distance above it. The fact that the maximum girth does not 

 coincide with the actual base, renders the term "mound- 

 shaped" not perfectly applicable, and admits of a distinction 

 into an extensive upper surface, and a restricted lower 

 one. From the former there arise few or many elevations in 

 the form either of short digitiform processes, or of compressed 

 ridges. The interior of the sponge, to within a few milli- 

 metres of the surface, is traversed by numerous rather wide 

 canals, some of which attain a diameter of 10 mm. ; they are 

 lined by a distinct aspiculous membrane, which also forms 

 dissepiments across their lumina. The central peak is pene- 

 trated to its apex by one or several of these canals, which 

 terminate in a corresponding number of oscula. Occasionally 

 a few of the secondary elevations are similarly provided, but 

 usually they contain only minor branches of the canal system. 



