316 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



to 125 \i long occur. The inclination of the clads away from the 

 orthotriaene state is not great in this spicule. 



The plagiotriaenes occur in the radial bundles. They are not at 

 all abundant although their presence is constant. The cladome is 

 at the surface of the sponge or sometimes within the sterrastral 

 layer. In flat preparations the cladomes appear rather scantily 

 strewn over the surface. 



Quite small ones, with rhabdome only 20 \l thick and cladi 40-70 

 [x long, occur scantily in the choanosome, the cladomes lying in the 

 subcortical zone. These are doubtless young stages. 



3. Anatriaene. Rhabdome long, 8-15 \x thick above; clads 25-50 

 [i long; cladome rather shallow. Projecting radially from the sur- 

 face. A large proportion of the spicules that project conspicuously 

 (several millimeters) beyond the surface are anatriaenes. What are 

 doubtless young stages occur scantily in two positions: (a) cladome 

 in the subcortical zone; rhabdome 4 jx thick, ciads 7-14 \i. long; (b) 

 cladome among the projecting ectosomal oxeas; rhabdome 2 [i thick 

 above, clads only 4 \l long. 



4. Protriaene. Rhabdome long, 15-20 \x thick above, clads 50-70 

 pi. long. The rhabdome is occasionally prolonged beyond the inser- 

 tion of the clads, the spicule becoming, in Lendenfeld's terminology, 

 a promesotriaene (pi. 46, fig. lb). The protriaenes occur scantily 

 among the spicules projecting beyond the surface. 



5. Ectosomal and subcortical oxeas; 210 by 4-7 \l; piercing and 

 projecting more or less radially from the dermal membrane; here 

 abundant, the spicules disposed singly or in loose sheaves. The same 

 spicule occurs sparsely in the subcortical zone, usually in a radial 

 position. 



6. Sterraster. Slightly flattened, thickness about five-sevenths 

 greatest diameter; in face view varying from nearly circular to ellip- 

 tical: dimensions as seen in face view, 144 by 136 \j. (approximately 

 circular) to 193 by 155 y. (elliptical). The circular shape, in face 

 view, may possibly be reached, but a number of measurements 

 showed a discrepancy between the two horizontal axes. In face view 

 the shape is sometimes slightly oval instead of elliptical. 



The layer of sterrasters occupies nearly the whole thickness of the 

 cortex, 1.5-2 nun. thick. The spicules are also scattered, together 

 with young stages, through the choanosome. The development is of 

 the usual type. 



7. Dermal oxyaster; 4 jjl in diameter: with relatively large cen- 

 trum and short conical rays. Very abundant in dermal membrane. 



8. Oxyaster of subcortical zone; also lining the lower part of en- 

 dochonal canal. Total diameter 24-40 \i.. Centrum distinctly de- 

 veloped. Rays long, tapering, spinose at extreme end, the end of the 



