126 



GEODIA AGASSIZII. 



from Station 4228 are, at the cladome, 9-13 ji thick, the maximum average of 

 this dimension being 12 p.. The clades are conical, pointed, and always curved, 

 concave towards the epirhabd, in their basal part. In their distal part they are 

 either curved in the same direction (Plate 28, figs. 3, 5, 6), or nearly or quite 

 straight (Plate 28, figs. 2, 4, 7; Plate 32, figs. 40, 41), rarely abruptly bent 

 (Plate 28, fig. 1). The angles between the chords of the clades and the 

 epirhabd are in the mesoprotriaenes of the adult specimens 22-55°, on an average 

 38°. The mesoprotriaenes of the specimens from Station 4193 have exceptionally 

 large, those of the specimens from Station 2886 exceptionally small, clade- 

 epirhabd angles. As a rule the three clades of the same cladome are fairly equal 

 in size; mesoprotriaenes with unequal clades are, however, by no means rare. 

 Sometimes their inequality is so great that the longest clade of a cladome is 

 more than twice as long as the shortest. Sometimes one clade is reduced to a 

 mere knob, and the spicule appears as a promesodiaene. A few such promeso- 

 diaenes I found in the spicule-preparations of the young specimen from Station 

 4228. The rhabdomes of these spicules are much stouter and their clade-angles 

 much smaller than those of the mesoprotriaenes and it is possible that they are 

 foreign to the sponge. The chords of the clades of the mesoprotriaenes of the 

 adult specimens are 60-250 n long, their average maximum length being 161.78 

 1.1. The longest clades are observed in the mesoprotriaenes of the specimens 

 from Station 2978, the shortest in those of the specimens from Station 4193. 

 The chords of the clades of the mesoprotriaenes of the young specimen from 

 Station 4228 are 95-125 p. long (maximum average 120 p) and enclose angles of 

 about 42° with the axis of the epirhabd. 



The epirhabd is straight, conical, and pointed. In the majority of the 

 mesoprotriaenes it is about as long as the clades (Plate 28, figs. 1-6; Plate 32, 

 figs. 40, 41). In not a few, however, it is either considerably shorter or con- 

 siderably longer (Plate 28, fig. 7). It is in the adult specimens 25-320 ji long, 

 its average maximum length being here 140.33 p. Of all the spicule-cUmensions 

 the length of the mesoprotriaene-epirhabd is the most inconstant, the differ- 

 ences of the adult specimens from the nine stations in this respect being very 

 great indeed. The longest epirhabds are met with in the mesoprotriaenes of 

 the specimens from Station 4199, the shortest in those of the specimens from 

 Station 4193. In the young specimen from Station 4228 the epirhabds of the 

 mesoprotriaenes are 85-100 p long, their average maximum length being 95 p. 

 In the immature specimen described by Lambe the rhabdome is 20 p thick, the 

 clades are 60-90 p. long, the clade-angles are 36-47°, and the epirhabd is about 

 70 [1 long. 



