18(57.] DU. J. S. BOWEKUANK ON HYALONEMA MIRABILE. 33 



are all of the same species, and that the basal mass and the spiral 

 cloacal organ are truly parts of the same individual. 



The external mammillated coriaceous dermis of the cloacal system 

 in the dried condition closely embraces the spiral column of spicula, 

 but I could not detect any organic connexion between them. It is 

 probable, from its reticulated structure in some parts, that there 

 was a considerable intervening space between the spiral column and 

 the external envelopment while in the living state, and that the pre- 

 sent condition is due to the contraction of the coriaceous coat while 

 drying. 



DESCRIPTION' OF PLATES lY. & V. 



Pl-ATE lY. 



Fig. 1. Hyaloncma mirabile in the ciibinet of C'apt. Charles Tyler, having a small 

 basal mass of sponge covered with the dermal membrane, which is 

 continued up the spiral column, and from which protuberant oscula 

 are put forth. Natural size. 



Fig. 2, A specimen of the same species of Sponge presented to me by Mr. H. 

 Lee. The basal mass of sponge is without the dermal membrane, but 

 having the commencement of the corium corresponding with the distal 

 end of the spongeous mass. Natural size. 



Fig. 3. A section at right angles to the long axis of one of the oscular organs, 

 just below the corrugated terminal disk, exliibiting a view of the inte- 

 rior of the upper portion of the dissepimental form of the complicated 

 valvular structure within the apical termination of the oscular tube. 

 The central membrane containing the natural orifice is slightly in- 

 volved, .showing on its outer surface a portion of the sand imbedded. 

 By direct light, magnified 50 times linear. 



Fig. 4. The lower portion of the valvular structure of the same section, showing 

 the inner diaphragm, or valve, with its motive filaments. The valve 

 partly open, and its membranous structure having a cruciform spicu- 

 lum imbedded in its substance at a. By transmitted light in Canada 

 balsam, magnified 50 times linear. 



Fig. 6. The apical termination of one of the oscular tubes cut off immediately 

 beneath the corrugated ajiex, after maceration in solution of potass, 

 showing the circular arrangement of the motive fibres of the outer 

 valve of the osculum in situ, and tlie attachment of their apices to the 

 outer margin of tlie central oscular membrane, their basal portions 

 curving downward at the outer margin of the corrugated apex of the 

 organ to their respective basal attachments. Mounted in water and 

 viewed by transmitted light, magnified 50 times linear. 



Plate Y. 



Fig. I. One of the lamellae of the skeleton from the basal mass of sponge of 

 Hi/alonema mirabile in the British Mu.seum, exhibiting the general 

 structure of the skeleton and the mode of disposition of the fimbriated 

 multihamate birotulate spicula, the spiculated cruciform, and the 

 various forms of interstitial spicula. a. One of the large.st of the at- 

 tenuato-rectangulated hexradiate interstitial spicula in situ, with a 

 group of three fimbriated multihamate birotulate spicula, and spicu- 

 lated cruciform spicula dispersed on the transparent interstitial mem- 

 branes, b^ Skeleton-fasciculi, with a row of spiculated cruciform 

 spicula based on one of them. Magnified 50 times linear. 



Fig. 2. A fimbriated multihamate birotulate interstitial spiculum of the primarv 

 system. Magnified 175 times linear. 



Fig. 3. An clongo-recurvate dentato-birotulate inter.siitial spiculum of the se- 

 condary system. Magnified 308 times linear. 



Proc. Zool. Soc.~1867, No. III. 



