108 THE SPONGES. 



able number beneath the dermal membrane of the oscular surface, and in 

 small number beneath that of the pore surface. 



h. Rhaphid form, about 3.5 mm. x 10 /-i ; smooth, nearly cylindrical, 

 though tapering at the ends ; slightly curved. Much less abundant than 

 the stouter form, with which the spicule occurs intermingled. 



2. T?iaeiie, Fig. 10, Plate 14. Rhabdome about 200 ju, x 30 /x, straight, 

 smooth, pointed. Cladi about 380 fx x 30 /a, slightly arched outward, 

 smooth, tapering to points. Lying in the ectosome, the cladi extending 

 tangentially beneath the dermal membrane. The spicules are only sparsely 

 present at the pore surface; more abundant at the oscular surface, in places 

 quite abundant, although forming only a single layer ; most abundant 

 round the free edge of the sponge, where the cladi may form in spots two 



or three layers. Triaenes (Fig. 9, Plate 14) are occasionally found 



in which one or two of the cladi are forked (imperfect dichotriaenes). Or 

 one of the cladi is bent as if only one of the deuterocladi had developed. 



Such a spicule is shown in Fig. 3, Plate 15. In a large number of 



preparations, I found only a single triaene, and that, like those at the 

 surface, in the interior of the sponge. 



Microscleres. 



3. Microxea, Fig. 11, Plate 14. Spicule about 180 ^ x 4 /x, slightly 

 curved and tapering gradually toward each end ; surface minutely rough- 

 ened. The spicule may be symmetrically curved, or the curvature may 

 be slightly irregular. Exceedingly abundant in the ectosome, and here 

 chiefly tangential ; also very abundant in the trabeculae of the choanosome. 



4- Spirasier, Fig. 12 a, Plate 14. Spiral axis showing in projection 

 two or three concavities on the same side. Spicule length, 16 fx ; rays, 

 2-3 |U and tapering to sharp points. Very abundant in the dermal mem- 

 brane of both surfaces. 



5. Plesiaster (Fig. 12 Z», Plate 14) and plesiaster-mei aster (Figs. 12 c, 

 12 c?, Plate 14). Spicule length, 24 ^ ; rays straight, smooth, slender, 

 tapering to points, 12 ^ long. Axis smooth and short. The forms in 

 which the axis bears only rays at the ends are designated plesiasters; 

 number of rays commonly 5. When the axis bears rays at its ends, and 

 one or two along its course, the spicule is designated a plesiaster-metaster ; 

 number of rays commonly 6-7. The two varieties are intermingled, and 

 are abundant though not crowded throughout the choanosome. 



Now and then spicules are found with shorter and more numerous rays 



