SILICIOUS AND HORNY SPONGES WILSON. 401 



differentiated. These lie about 1 mm. apart, roughly parallel to 

 one another and to the two surfaces of the vase. The meshes of 

 the lamellae are small and the texture is fine; characteristic meshes 

 measure 80, 60, 40 [x in width. Between the lamellae the frame- 

 work is coarser; the fibers often 140-175 [/. thick, characteristic 

 meshes measuring 1.0, 0.7, 0.5, 0.4 mm. in width. 



The skeleton of the ectosomal region is finer and more regular than 

 that of the interior, showing radial fibers and transverse connectives. 

 There are some minor differences between the dermal skeleton of the 

 exterior and that of the cloacal wall. Thus the meshes of the skele- 

 tal reticulum covering the outer surface are commonly 175-350 [jl 

 wide, while those of the reticulum lining the cavity measure about 

 175-260 [jl in width. There are more projecting tips of radial fibers 

 on the inner than on the outer surface (due to wearing?). The 

 strands of the reticulum on both surfaces are mostly 3-5 spicules 

 wide. There is for the most part one pore in each mesh of the retic- 

 ulum. 



The characteristic spicule is an intermediate, 385-400 by 20 lj., 

 smooth, slightly curved, ends tapering but rounded off instead of 

 pointed. Strongyles of same size, with ends evenly rounded off, also 

 occur. Sharp-pointed oxeas occur among the spicules of smaller 

 sizes. 



PETROSIA TESTUMNARIA, var. FTSTULOPHORA, new variety. 



Plate 40, fig. 5 ; plate 41, figs. 1, 2 ; plate 48, fig. 8. 



Three dried specimens from stations D5249, D5253, D5254, and 

 alcoholic fragments from D5253 and D5254 constitute the material 

 on which this variety is based. The essential difference from the type 

 lies in the fact that the outer surface bears fistular processes instead 

 of vertical ridges, but there are intergrading individuals. 



The sponge from station D5254 (pi. 41, fig. 1) represents the ex- 

 treme amount of divergence from the type. It is an oblate spheroidal 

 mass about 300 mm. wide and 160 mm. high. It was attached by the 

 whole under surface, which is somewhat convex and rough. The 

 crateriform cavity, opening on the upper surface, is small, only 100 

 mm. wide and 60 mm. deep. Sponge is light brown, darker inside; 

 firm, but in the dried state easily broken; considering its bulk, not 

 heavy. 



The outer surface bears very numerous radiating hollow projec- 

 tions, which may be designated as fistular processes. These are 

 15 mm. or less apart, somewhat flattened in the meridional plane 

 and closed at the outer end by dermal membrane. A typical process 

 measures 15 mm. in height, with cross diameters of 20 and 12 mm., 

 the long cross diameter lying in a meridional plane of the sponge; 

 wall of the process about 3 mm. thick. The cavity in each fistular 

 81709—25 10 



