166 



GEODIA OVIS. 



interesting as hcxactinc abnormal megascleres are exceedingly rare in tetraxonid 

 sponges. 



The mesoproclades and their proclade derhates (Plate 43, figs. 1-8) have a 

 rhabdome 6-17 mm-, long and, at the cladome, 20-41 pt thick. At its thickest 

 point, which lies a little above (nearer the cladome than) the middle of the length 

 of the rhabdome, the rhabdome is from two to three times as thick as at the 

 cladome. The cladomes of these spicules are very variable. Triaene forms 

 greatly predominate. In the most regular mesoprotriaenes (Plate 43, figs. 3, 4) 

 the clades are fairly equal, conic, blunt pointed, slightly curved, concave to the 

 epirhabd, and 140-170 fi long. Their chords enclose angles of a little over 45° 

 with the axis of the epirhabd. The epirhabd is straight, conic, about 110 }i 

 long, and pointed at the end. Mesoprotriaenes with cladomes rendered irregular 

 by the clades being of unequal length (Plate 43, figs. 6, 8) are very abundant. 

 In these spicules one clade may be very much longer than the other two, which 

 latter again may be fairly equal (Plate 43, fig. 6) or very unequal (Plate 43, fig. 8). 

 In these irregular mesoprotriaenes the clades are 40-260 pt and the epirhabd 

 is 70-100 n long. 



In some of the mesoproclades one or two clades are completely suppressed; 

 these appear as mesoprodiaenes (Plate 43, fig. 1) and mesopromonaenes. The 

 dimensions of the clades and epirhabds of these spicules are similar to those 

 of the triaene forms. The clades of the mesoprodiaenes are not opposite each 

 other but occupy the same positions — in planes passing through the rhabd- 

 ome and enclosing an angle of 120° — as they would if the third clade were 

 present. 



Some of the teloclades observed I am inclined to consider as mesoprotriaene- 

 derivates in which the epirhabd has been suppressed. These spicules have a 

 rhabdome as long and thick as or slightly thicker than the mesoproclades, and 

 three more or less ascending clades, convex to the rhabdome, the chords of 

 which are 100-360 }i long and enclose angles of 31-76° with the continuation of 

 the rhabdome-axis. The large-angled forms of these spicules (Plate 43, fig. 2) 

 appear as plagioclades, the small-angled ones (Plate 43, fig. 7) as proclades. 



The anaclades (Plate 42, figs. 2c, 3b, 10, 11, 23b, 24b, 25-40) are nearly all 

 anatriaenes. I have observed only one or two anamonaenes among them. 

 The anaclades are remarkable for the great differences in their size. The small 

 ones observed cannot be considered as the young of the large ones, because they 

 arc found in abundance, more or less extruded from the sponge, in the spicule- 

 fur, where they can hardly be expected to continue to grow. 



