32 



THE SPONGES 



shallow, and with noticeably flat tops. The umbel depth is commonly 

 about \ the total length. The total length is the same as in the other 

 specimens. A typical macramphidisc of this specimen is shown in Pig. 7 ? 

 Plate 1. 



The macramphidiscs are very abundant in the dermal and 



gastral membranes of all specimens. A few are found in the internal 

 parenchyma, but this position may not be natural. 



Mingled with the characteristic 8-rayed macramphidiscs are a consider- 

 able number of amphidiscs of the type shown in Figs. 10 and 11, Plate 1. 

 The umbel is usually 4-rayed, but umbels with 5 and 6 rays occur. The 

 shaft is smooth, and the umbel rays very similar to those of the 8-rayed 

 form. The spicule varies somewhat as regards the precise shape of the 

 umbel, which in some spicules (Fig. 10) is deeper than in others (Fig. 11). 

 The total length is 60-100 /z. It is possible that these spicules represent 

 young stages of the 8-rayed form. 



Mesamphidiscs (Fig. 4, Plate 1), 50-80 /x long, are abundant. The 

 shaft bears scattered small tubercles in varying number. The umbel is 

 deep bell-shaped, with 8 pointed and rather narrow rays. The umbel 

 depth is slightly more than J the total length. 



Micramphidiscs of the common Ihjalonema type, 20-25 /x long, are 

 abundant. Intermediate forms between these and the mesamphidiscs are 

 common, and especially abundant in the walls of the main efferent canals. 



Pathological amphidiscs of small size are occasionally observed, similar 

 to those described by Marshall and Meyer, 1879, p. 261, Taf. XXV 

 Figs. 19, a, b, c. In one such, which measured 72 tt in total length, 3 rays 

 of the hexact had developed umbels which were not quite alike, one ray 

 was club-shaped at the end, and a fifth ray had the form of a short spine. 



The lower end of the body is well preserved in only one specimen, 

 that from Station 3376. The collar-pad here bears on its outer surface 

 the ordinary dermal skeleton, but round the root spicules there is a thick 

 dense layer of acanthophorae. In these, only the ends of the rays are 

 spinose. The ends are frequently but not always slightly enlarged. The 

 spicules include diacts, tauacts, stauracts, pentacts, and hexacts. Stauracts 

 with subeqtial or very unequal rays are the commoner forms. In a repre- 

 sentative diact, the total length is 900 p. In a typical stauract the length 

 of the longest ray is 250 //,. 



The basalia vary in greatest diameter from 130 ^ to 1 mm. The 

 spicules in their lower portions taper rather rapidly and over a consid- 







\, 



JM 





-.-■Vv 



