56 DR. G. J. HItfDE ON CALCISPONGES [Feb. I9OO, 



(PI. IV, fig. 10). The upper surface of the sponge exhibits spicules 

 of the same character as in the interior ; the three facial rays are 

 connected with those of adjacent spicules, so as to mark off small 

 rounded or subangular interspaces, while here and there are distri- 

 buted the larger rounded canal- apertures. The projecting apical 

 ray of the spicules is short and inconspicuous at the surface. 



In a small region near the base of the sponge the mesh is built 

 up of more delicate spicules, and the interspaces are closer than in 

 the rest of the skeleton (PI. IV, fig. 11) ; with this exception the 

 proportions of the fibres are fairly uniform, but they slightly tend 

 to become thicker in the upper part of the sponge. Simple fibres, 

 of a single spicular ray, are about O05 mm. thick, while those 

 in which two or more rays overlap one another reach to 0*1 mm. 

 in thickness. 



In the interspaces of the skeletal fibres numerous slender spicules 

 are distributed, either singly, in small aggregates, or in tufts or 

 wisps, in which the spicules are generally parallel. These spicules 

 are almost exclusively cylindrical or slightly fusiform rods, pointed 

 at both ends, either smooth or having surfaces studded over with 

 minute spines (PI. Ill, figs. 39, 39 a, 46, 47). Some are exceedingly 

 delicate, and yet as perfect as in recent sponges. They vary in 

 length from 0*04 to 0*42 mm., and in thickness from 0*002 to 

 0-004 mm. 



Of rare occurrence are straight, styliform, and pin-shaped spicules, 

 with somewhat tumid heads, smooth surfaces, cylindrical or slightly 

 tapering shafts, and pointed ends, which are either from the 

 inner portion of the dermal layer or associated with the simple 

 pointed rods of the mesh-interspaces (PI. Ill, figs. 40-42). They 

 measure from 0*13 to 0*2 mm. in length, and about 0*004 mm. in 

 thickness. 



Canal-system. 



No definite incurrent pores or canals can be recognized in the 

 skeleton ; on the other hand there is a well-marked system of 

 excurrent canals, which take their rise in the lower portion of the 

 sponge and extend in a generally vertical or radiate direction to 

 open out at the summit (PL III, fig. 1 a). Some canals also appear 

 at the side of the sponge, near the upper margin of the dermal 

 layer, and are continued as open furrows over the summit- edge. 

 The walls of the canals are formed by the ordinary spicular fibres, 

 and they are in free communication with the interspaces of the 

 mesh. Numerous free cylindrical spicules occur within the canals, 

 just as in the mesh-interspaces ; in places they are so abundant 

 as to give an idea that they may have formed an inner lining to the 

 canal-walls. The canals range from 0*2 to 0*5 mm. in width. In 

 the central area of the sponge-summit they are about their own 

 diameters apart, but apparently at somewhat wider intervals 

 towards the margins. 



