SILICIOUS AND HORNY SPONGES WILSON. 369 



size, are scattered abundantly through the choanosome. The 

 tangential ectosomal oxeas are like those of the choanosome. 



2. Protriaenes. (a) Protriaenes, prodiaenes, and promonaenes 

 occur abundantly in the radial bundles, the promonaenes and pro- 

 diaenes being especially conspicuous and characteristic. The 

 rhabdome in these spicules is about 4 mm. by 16-24 \l; clads with 

 a basal thickness about equal to that of rhabdome. The single clad 

 of the monaene, whch in some specimens (station 5478) may be 

 irregularly curved in and out, is 200-350 [x long; on the under 

 surface (station 5134) it may reach 500 \l in length; very rarely it is 

 dichotomous (station 5478). In the diaenes the clads are 120-250 p 

 long; very rarely the clads may spread out almost at right angles 

 to the rhabdome. In the protriaenes the clads are in general 

 shorter and slenderer than in the prodiaenes, but the range in size is 

 about the same. Any or all of these protriaenes forms may project 

 a short distance beyond the surface of the sponge. 



(b) Protriaenes of a stouter type project from the radial bundles 

 in some abundance over the general surface and occur among the 

 root spicules; rhabdome long and 20-35 p thick; clads shorter and 

 relatively stouter than in type a, 50-100 [x long; one clad sometimes 

 aborted. 



(c) Protriaenes of the fringes round the apertures of the pori- 

 ferous pits have a long rhabdome, 9-10 mm. long, 16-24 jx thick, 

 with clads 100-175 y. long. Smaller ones also occur. From the adja- 

 cent part of the lateral wall of the pit quantities of very small trich- 

 odal protriaenes project obliquely upward. 



3. Anatriaenes. (a) In the anatriaenes of the radial bundles in 

 general the rhabdome is 5-10 mm. long, 8-12 \l thick, then becoming 

 hair-like; clads 20-50 \l long. These spicules are not abundant in 

 the preparations made from some specimens (station 5152) but 

 are more abundant in those made from others (stations 5134 and 

 5179). Many project beyond the surface. 



(b) Anatriaenes of the under surface reach a larger size than 

 those of the upper and lateral surfaces and are also more abundant, 

 many projecting. They form the chief element in the root bundles. 

 The rhabdome measures about 10 mm. by 20 jjl, clads 40-90 y. long. 



4. Sigmas. In the ectosome and adjoining zone of the choanosome, 

 the sigmas, which are very abundant, measure commonly 28-36 [i 

 in length, the spiral being long and open and generally showing two 

 convexities; smaller ones are intermingled. The spicule is frequently 

 so bent in the middle (see Ghrotella macellata Sollas) as to have 

 something of the appearance of a toxa. In the choanosome in gen- 

 eral the sigmas are shorter, about 16 [l long, and of the typical 

 simple contort shape. 



81709—25 8 



