SILICIOUS AND HORNY SPONGES WILSON. 397 



attention has not been called, and which may not be constant. It 

 is conspicuous when the sponge is examined with a lens. From each 

 conulus radiate a number of narrow ridges, all combining to form 

 a fine dermal reticulum, composed of ridges or of trabeculae which 

 are not elevated, between which lie thinner areas of dermal mem- 

 brane riddled with pores. The ridges and trabeculae are denser 

 and more fibrous than the rest of the dermal membrane; they are 

 not supported by a skeletal reticulum. This reticulum is essen- 

 tially the same as that found in many horny sponges, where the 

 varying appearance of the surface in the same specimen indicates 

 that the reticulum, which is conspicuous when the pores are open, 

 may disappear when the pores have been closed for a considerable 

 time. It offers a striking case of analogical resemblance between 

 widely distant sponges. 



As in the already described specimens, the spicules of the interior 

 are both scattered irregularly and combined in loose tracts. The 

 ectosomal tracts which extend into and support the conules, slightly 

 projecting beyond the apices of the latter, may be radial or quite 

 oblique. Save for these, the dermal membrane is almost free of 

 spicules; it contains only a few scattered ones. Perhaps this is a 

 variable feature, for Lindgren (1898, p. 285) says: "In the dermal 

 membrane the spicules are quite without order." 



The oxeas are slightly curved, taper gradually to sharp points 

 and commonly measure 650-770 by 24-30 [/.. A slight irregularity 

 of curvature is present in some of the spicules (would it not be 

 found, on searching, in other species?). A more definite, doubtless 

 local, peculiarity is a feeble annulation exhibited by some of the 

 spicules, which may or may not be in the middle. 



It may be noted that some of the north Atlantic Halichondrias 

 have also differentiated ectosomal spicular tracts which support 

 the dermal membrane on their projecting ends. This resemblance 

 of these species {H. oblonga and H. tenuiderma, Lundbeck, 1902, 

 pp. 24, 26) to the East Indian form is probably only analogical — 

 namely, due to the independent occurrence and fixation of the same 

 variation in organisms having a common basic constitution. 



Genus RENIERA Nardo (1847). 



Renicra Nardo, 1847. — O. Schmidt, 1S70, p. 39. — Ridley and Dendy, 1SS7 , 

 p. 14. 



Skeleton typically a close and uniform reticulum, each side of the 

 polygonal mesh formed by a single spicule. Spongin usually at the 

 nodes of the reticulum. The side of the mesh may however be 

 inultispicular, and long multispicular tracts may develop. 



