25 



inflation, from wliicli four rounded protuberances, arranged crosswise, arise. 

 Sometimes these extend to form curved spines. 



Macramphidiscs are met witli in tlie dermal membrane. They attam a 

 length of 300 ^ , their terminal discs are relatively flat and 130 i^ broad, and 

 have S spade-like marginal teeth. The shaft has a considerable thickness (20 m). 

 It is covered with low, irregularly-scattered tubercles and bears in the centre 

 four rounded protuberances, ari^anged crosswise (pi. VI, f. 3). Certain amphi- 

 discs 40-50 /^ long and 15 /^ broad, which are met with pretty frequently in 

 some places, I consider as mesamphidiscs. Their terminal discs are hemispherical, 

 about 16 M long and have 8-12 marginal teeth. The shaft is not pai'ticularly 

 stout, distally smooth, thickened and often also spined in the middle (pi. VI, f. 5). 



The micramphidiscs are numerous, 20-30 M long and similar to the micramphi- 

 discs of other species of Hyalonema. Besides these ordinary ones, micramphi- 

 discs of about equal length (15-20 i^ ), but greater breadth (10-12 /^ ) and essen- 

 tially different in shape, occur in Hyalonevia alcochi. As these spicules have been 

 observed for the first time in this sponge I think them worthy of a detailed 

 description. They are on the whole similar to ordinary amphidiscs but differ 

 from them fundamentally in that they are not radially symmetrical and have 

 an excentric shaft. "We can imagine that they have originated from ordinary 

 amphidiscs by the atrophy of one half of the one and the opposite half of the other 

 terminal disc. Such an atrophy must cause a change of the position of the shaft, 

 relative to the terminal discs : it connects no longer their centres in a direction 

 vertical to them, but lies obliquely, extending from the margin of one of the 

 discs to the opposite margin of the other. The eight typical marginal teeth of 

 the terminal discs have also lost their radial symmetry. On the side where the 

 disc has attained its full development they are rather larger : towards the oppo- 

 site, reduced side, they become smaller and smaller, the last two (in the middle of 

 that side) having disappeared altogether. Thus the peculiar Z-shaped spicules 

 illustrated on plate VI, figs. 4a, 46, 12-16, which I shall henceforth designate as 

 " paradises, " are produced. Sometimes the teeth are uniformly rudimentary all 

 round, then the terminal disc appears as a shield- or egg-shaped plate with con- 

 tinuous margin, but also in this case it is clearly to be seen that the disc is 

 reduced on one side and elongated on the other (pi. VI, f. 11) and that the posi- 

 tion of these deformations is reversed in the two opposite discs. The shaft of 

 the paradise has, in the centre, either a simple, spindle-shaped thickening (pi. 

 VI, f. 4a, Mi), or four button-shaped protuberances, arranged crosswise (f. 15), 

 or it is covered with scattered, rounded tubercles (f. 16) throughout, or finally it 

 is a simple, smooth cylinder (f. 11, 12). 



The parenchymal microhexactines are numerous, and have smooth, strongly 

 curved rays, about 60 i^ long. 



The acanthophores of the basal part of the body are of varying size and 

 4 



