31 



I shall now describe the five doubtful species of which only young speci- 

 mens were at my disposal. 



Ryalonema aculeatum F. E. Sch. 

 Plate II, Figs. 1-14. 



1895 Hyalonema aculeatum P. E. Sch. in Abh. Preuas. Ak. 1894 p. 19, Taf. Ill, Egs, 1-14. 



Four of the numerous Hyalonemas found in the Andamans have remarkably 

 long prostalia lateralia, so that I first supposed them to be young Pheronemas. 

 This supposition appeared supported by the slender pear-shaped form of their 

 body and the presence of a slender tuft of long basal spicules which protrude 

 from its lower end, peculiarities which also appertain to the young Pheronema 

 caiyenteri described by Wyville Thomson and figured by him in the Philosophical 

 Transactions for 1869 on plate LXXI. Closer investigation showed, however, 

 that this sponge is not a Pheronema but a Hyalonema, The high central cone, 

 the regularly-quadratic dermal reticulation, and the absence of bidentate anchor- 

 spicules and simple uncinates exclude it from the genus Pheronema. The general 

 structure, and particularly the shape of the spicules, are in accordance with 

 Hi/alouema. There is therefore nothing for it but to extend the genus Eijalovema 

 as indicated above, so as to comprise not only smooth forms but also sponges 

 rendered spiny by the presence of prostalia lateraha. The name Hyalonema 

 aculeatum has been given to these sponges on account of their freely-projecting 

 spicules, which render them spiny. It must be taken into account however that 

 they are, in all probability, young forms which may possibly lose their prostalia 

 lateralia on attaining maturity and then become just as smooth and spineless as 

 the other species of Hyalonema. I do not consider this probable however, be- 

 cause the smallest of the very unequally sized specimens at my disposal does not 

 possess more prostalia lateralia than the others. On the contrary, the number, 

 size, and areas occupied by the lateralia increase with the growth of the sponge, 

 as is shown in fig. 1-4 of plate II, in which these sponger are represented. 



The smallest of the four specimens measures 7 mm. in length and 5 mm. in 

 breadth, the largest is 14 mm, long and 10 mm, broad. Although not very con- 

 stant in shape, they all resemble a turnip with considerably attenuated lower 

 end. From this a root-tuft, 2-4 cm. long, up to 1 mm. thick, and lying in the 

 prolongation of the axis of the sponge, protrudes. The broader upper end is 

 covered by a dome-shaped continuation of the dermal membrane- In the two 

 smaller specimens this is continuous, in the two larger ones it is perforated by a 

 small circular oscule with sharp margin, which latter however is not raised to 

 form a vertical oscular fringe or collar. The prostalia lateralia are confined to 

 the broad upper part of the body ; in the small specimens they are 5-10, in the 

 laro-er ones 10-20 mm. and more long. With the age of the sponge they in- 



