SIL.ICIOUS AND HORNY SPONGES WILSON. 299 



inner zone of the ectosome is densely fibrous and 40-60 [x thick; in 

 it the pigment cells are only scantily present and distinctly flattened. 

 Above the fibrous layer the ectosome contains abundant small 

 rounded subdermal spaces, into which the pores open directly, pierc- 

 ing the dermal membrane. The subdermal spaces connect at the 

 level of the fibrous layer with larger spaces, the subcortical crypts. 

 These are more conspicuous than the subdermal spaces. The ar- 

 rangement constitutes a variant of that shown in Sollas' diagram 

 (fig. 7, A, p. xxiv, 1888). The choanosome contains some canals 

 of relatively good size, but in general is compact. 



The radial skeletal bundles are closely set, expand at the surface, 

 converge internally, but by no means reach the center of the sponge. 



The spicules closely approximate in shape and measurements 

 those of Thiele's specimens, as will be seen from the following: 



1. Skeletal oxea, reaching 2.5 mm. by 60 jx ; in radial bundles, also 

 scattered. 



2. Plagiotriaenes, in radial bundles. Rhabdome 1.5-2 mm. by 

 60 \l. Clads in general lie at the surface; strong, 120-175 [x long. 

 Younger ones, as usual, with cladomes deeper in the ectosome or 

 in the outer part of the choanosome. Thiele (1900, p. 32) desig- 

 nates this spicule an orthotriaene ; length of clad about 250 [x. But 

 his figure shows that it is assignable to the category of plagiotriaenes, 

 where Lendenfeld (1903) puts it. 



3. Anatriaenes, in radial bundles; abundant. Rhabdome 3 mm. 

 by 24 jx. Cladome deep, clads 80-120 [x long, strong. Cladomes gen- 

 erally in ectosome, close to the surface. 



4. Protriaene. Rhabdome 15 |x thick, clads 40 [x long. Only one 

 found protruding from the surface; the sponge was well searched 

 over for this form of spicule. The protriaene may possibly be only 

 an occasional variant of the characteristic triaene. Or, as Thiele 

 suggests, it may possibly be a fairly constant element in the spicula- 

 tion of the genus, though usually broken off and overlooked. 



5. Ectosomal oxea, 250 by 3 [x. Radial to the surface, in ectosome. 

 Abimdant, but the individual spicules spaced well apart from one 

 another. The spicule is equiended, this feature constituting a min- 

 ute point of difference from Thiele's specimens. 



6. Microstrongyles. Straight, a little thicker in middle than at 

 ends, minutely roughened ; 10-12 jx long by 2-3 jx. Crowded at, and 

 close to, the surface, forming a dermal crust. Scantily present 

 deeper in the ectosome and in choanosome. 



7. Chiaster, mostly about 8 [x diameter, with very small centrum, 

 and 6-9 long slender rays, not obviously tylote. Scantily present 

 in ectosome and choanosome. Larger ones, 12 jx in diameter, with 

 distinctly tylote rays, are occasionally found in choanosome. 



The form evidently can not be separated from Thiele's species. 



