CALCAREA. I7 



The Qiiadriradiates are of one sort : — 



[h) Regular quadriradiates of varying size from the lining of the excurrent 

 canals. Facial rays almost straight, tapering to a point 60 m to 180 m 

 long X 4 M to 8 m thick. Apical ray very slightly wavy, sharply pointed. 

 The point usually bent a little to one side, 50m to 120m long x 3m to 

 4 M thick. 



Leucandra gelatinosa. 

 (Plate XXX., Figs. 44-53.) 



There are two specimens of this new species in the collection ; one fixed in osmic 

 acid, which is therefore brown, and the other in spirits, which is quite white. The 

 consistency is firm and the surface smooth. The general shape of the larger specimen 

 shown in Fig. 44 is irregular and contorted, suggesting a tuberous root ; the oscule, 

 which is entirely closed, is at the top of the dome-shaped end. The diameter of this 

 part of the specimen is 1 1 mm. ; the smaller specimen is in the form of a rod 24 mm. 

 long, nearly straight, rounded ofi' at the oscular end, which is 4 mm. diameter, and 

 tapering gradually to the lower end, which is 2 mm. diameter. 



The mass of the sponge is formed of the solid gelatinous mesoderm, which is 

 remarkably developed in this species, and the incurrent and excurrent canals are reduced 

 to definite pipes lined with epithelium in this jelly. There is no gastral cavity, the 

 numerous excurrent canals converge to the oscule in the top of the domed end. These 

 canals are regular circular pipes of small section lined with an extremely, elastic 

 epithelium, which has contracted to such an extent as to almost close the lumens of the 

 canals (see Figs. 45 and 46). 



The flagellated chambers are scattered throughout the body of the sponge and 

 communicate with the excurrent canals by means of narrow outlet pipes. The outlet 

 pipes from several flagellated chambers usually join together before they open into the 

 main excurrent canals. These small outlet pipes are lined with elastic epithelium, 

 which is continuous with the lining of the main excurrent canals, so that when the 

 main canals close the small pipes are stretched out lengthwise in order to maintain their 

 connection with the central lumen of the main canal (see Fig. 46). 



There are a large number of small ostia (see Fig. 48), close together all over 

 the dermal surface (see Fig. 47), which communicate through narrow passages (see 

 Fig. 49) with irregular branching chambers under the dermal cortex; these in 

 turn lead into the incurrent canals which run as irregular pipes radially inwards, and 

 communicate with more regular circular canals running parallel to the axis of the 

 sponge. These canals have not contracted. The flagellated chambers are often situated 

 close against the incurrent canals, so that the communication is direct, presumably 

 through a pore cell which, in the contracted condition of the sponge, is closed. When 

 there is no incurrent canal near the chamber a narrow branch leads from the incurrent 

 canal to the flagellated chamber (see Figs. 51, 52 and 53). 



2 K 2 



