SIGMATELLA. 197 



met with. All these spicules are pretty straight. B. Signiata : exceedingly 

 abundant throughout the whole of the sponge, particularly in the canal-walls, 

 very small and slender, only 0*01 millim. long. Neither Marshall nor Carter 

 mention any proper picules. 



The cortex is not continuous, but appears as a reticulation of arenaceous 

 bands of varying breadth, the meshes between which are irregular, rounded, 

 and on an average 0*2 millim. wide. Fine membranes, which are free from 

 foreign bodies and which contain small spicules, chiefly small sigmata, are 

 spread out in them. In each of these membranes a single inhalant pore, 

 or a small group of two to five pores, is observed. The pores are 0*04:-0*l 

 millim. wide and mostly circular. They lead into pretty wide canals, which 

 penetrate the sand-cortex and open out into the subdermal cavities, which are 

 very narrow, only about 0-04 millim. wide. Inhalant canal-stems, 0-08 millim. 

 wide, with annular strictiu*es, arise from the subdermal cavities. These are 

 ramified, but do not give off numerous narrow branch-canals, their branches 

 being nearly as wide as the trunks. The ciliated chambers are supplied direct 

 from them. They are oval, about 0-07 millim. long, 0*04 miUim. broad, and 

 open with wide mouths into the exhalant canals, the narrowest of which are 

 over 0-08 millim. wide. The exhalants join to form canals which extend 

 longitudinally, 0-3 millim. wide, and often traversed by prominent strictures 

 in their walls. They bend round abruptly at a nearly right angle, and open 

 by a circular mouth, 0*4 millim. wide, into the central oscular tube. It may 

 perhaps appear doubtful whether the mouths of the exhalant stems should 

 not be considered as the true oscula, and the large vents on the surface as 

 praeoscula. The mouths of these exhalant stems are about 1 millim. apart, and 

 pretty uniformly distributed over the wall of the oscular tube. The oscular 

 tubes themselves are cylindrical, and extend from the superficial vent right 

 down to the base of the sponge. They have a uniform width of 6-8 millim. 

 throughout, appear regularly cylindrical, and follow the curvatures of the tubes 

 in S. a. tubaria, but always appear perfectly straight in S. a. fiahellum. 



Sigmatella australis, var. tubaria, Marshall. 



Dysidea tubulosa, H. J. Carter, " Some Sponges from the West Indies and 

 Acapulco," Annals and Magazine of Natural History, ser. 5, vol. ix. p. 275 

 (1882). 



Psammascus decijaiens, W. Marshall, " Ueber Dysideiden und Phoriospongien," 

 Zeitschrift fiir wissenschaftliche Zoologie, Band xxxv. Seite 93 (1880). 



The sponge consists of an irregular upright cylindrical tube, or more fre- 

 quently of a bunch of such tubes, which grow up from a common base. These 

 tubes attain a length of 200 millim. ; they are thickest a little way above the 



