LEUCANDRA. 11 



part are generally met with. These cylinders attain a length of 20 to 30 

 millim. and a diameter of 6 millim. The gastral cavity is narrow, only one 

 sixth to one fourth of the diameter of the outer cylindrical surface. Osculum 

 terminal, without frill. A great number of very fine gastral pores, which lead 

 into very minute parietal canals, open in the surface of the stomach. In longi- 

 tudinal sections through the wall these latter are hardly visible. 



The main mass of the skeleton is, in this species, quite different from that 

 of all other Calcarea ; it is composed of several layers of enormous longitudinal 

 diact spicules, which lie parallel to the outer surface. These spicules are coated 

 and united by a cement which consists of small, mostly sagittal, triact spicules. 

 The large diact spicules are spindle-shaped, either tapering to both ends or 

 inflated at the oral end, mostly shghtly curved, rarely straight, 1 to 3 x 

 0-15 to 0-2 millim. All diacts lie ixi a longitudinal direction, parallel to the 

 longitudinal axis of the body, but pointing a little outwards at the oral end. 

 They are situated in several parallel layers closely packed (ten to fifteen layers 

 in the thickest part of the body-wall). The small interstices between the diacts 

 are filled up by small triactSy which surround particularly the inner diacts sheath- 

 like. Most of them are sagittal, and parallel, with their basal ray, to the 

 longitudinal axis of the body, whilst both the lateral rays diverge towards the 

 oral side and often embrace the diact spicules. The unpaired angle 150° 

 to 170°, the paired ones 95° to 105". The straight basal ray measures 0'15 

 to 0"2 millim. in length ; its basal thickness is O'OOo to 0*008 millim. Between 

 the sagittal rays there are also single, irregular, rarely regular, triact spicules. 

 The sagittal tetracts clothe the whole inner surface of the gastral cavity and 

 the large canals, and are arranged regularly ; the basal ray points towards the 

 aboral side. They possess an unpaired angle of 160° to 170°, and two paired 

 angles of 95° to 100°. Their basal ray is 0*25 to 0*35 millim. long, straight, 

 their slightly curved lateral rays are 0-2 to 0-3 millim. long, and, like the basal 

 ray, only 0-005 millim. thick. The apical ray is two to six times thicker, that 

 is 0*01 to 0-02 or 0*03 millim. Its length varies, in the greater part of the 

 gastral cavity it is only 0*1 to 0-15 millim., but towards the osculum 0-3 to 

 0*4 millim. long. The entrance to the gastral cavity is in this way surrounded 

 just below the osculum by a circle of strong apical rays. 



Geographical Distribution. — East coast of Australia: Port Jackson 

 (Frauenfeld) ; Port Denison (^Ramsay). 



Leucandra typica, Polejaeff. 

 Leucandra typica, E. von Lendenfeld, " A Monograph of the Australian 

 Sponges. — Part III.," Proceedings of the Linnean Society of New South 

 Wales, vol. ix. part 4, p. 1130 (1885). 



