404 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



The skeletal framework includes main fibers, about 225 p. thick, 

 which ascend in the body wall, arching so as to radiate obliquely 

 toward both outer and inner surface. Somewhat thinner connec- 

 tives extend transversely between these, giving rise to a regular net- 

 work with rectangular meshes, commonly about 1 mm. wide. In a 

 longitudinal section of the sponge, the main fibers and connectives 

 present a very ladder-like appearance. The fibers are independent, 

 not associated together as parts' of a reticular lamella, as in P. tes- 

 tvdinaria. They consist of closely packed megascleres with a little 

 spongin. 



There is a dermal skeletal reticulum on both surfaces. Meshes in 

 the neighborhood of 300 \i wide, commonly 4 or 5 sided, with the side 

 formed by a tract of a few spicules or sometimes by a single spicule. 

 The tips of the radial skeletal fibers project; and at least where the 

 surface is well preserved, there are closely set small, radial bundles 

 or tufts, 60-120 \i high, composed of the very small megascleres, 

 which project from the tangential tracts of the dermal skeleton. 



The megascleres range from very large ones through all sizes to 

 verjr small ones. The total range observed was 420 by 20 \i to 32 

 by 6 p.. As in the other species with this skeletal peculiarity, the 

 spicules fall more or less in two classes, large ones and very small 

 ones. The common size for the large spicules is, in one specimen, 

 about 300 by 16 jjl, in the other 300 by 20 \i. For the small spicules 

 the common size is about 40 by 6 [x to 80 by 10 \t; The spicules (pi. 

 48, fig. 9) are smooth, slightly curved, and range from oxea to 

 strongjde; occasionally even a style (fig. 9, d) is formed. There are 

 some differences between the individual sponges as to the prevailing 

 shape of the spicules. Thus in the specimen from D5250 pointed 

 oxeas are absent or nearly so, the characteristic megasclere being a 

 strongyle in which the ends taper very slightly or not at all (fig. 9 a). 

 In the other specimen the characteristic large spicule is an inter- 

 mediate (fig. 9, b), with tapering ends which are not sharp but 

 rounded at the apex. But sharp-pointed oxeas (fig. 9 c, e) also occur 

 in abundance. The very small spicules (fig. 9, /) are in both speci- 

 mens strongyles or intermediates. They occur everywhere along with 

 the large spicules, but are especially abundant at the dermal surface, 

 in the projecting ends of the radial skeletal fibers and forming the 

 small radial tufts referred to above. 



HoIott/pe.—Csit No. 21283, U.S.N.M. 



PETROSIA LIGNOSA, var. PLANA, new variety. 



Plate 41, figs. 4, 5. 



Two dried vasiform sponges from Togian Bay, Togian Island, 

 Gulf of Tomini, Celebes, clearly belong to the above species but 

 differ conspicuously from the tj^pe in that the outer surface is smooth 



