90 THE SPONGES. 



present in small number, and chiefly in the neighborhood of the pore areas 

 and the osculum. 



3. Anatriaene ; rhabdome, 4 nmi. x 12 /a ; cladus, 2G0 /u. long. The 

 spicules range down to forms with rhabdome 2 mm. x 8 />i, and cladi 140 /z 

 long. 



The rhabdome is cylindrical, tapering gradually to the apex. The 

 cladome is deep (the sagitta longer than the chord), but the precise shape 

 of the spicules varies. The anatriaenes are only fairly abundant, occur- 

 ring in the parenchyma and in the fringes surrounding the osculum and 

 pore areas. 



^. Oxca. The very numerous oxeas which are abundant in the body, 

 roots, and fringes fall into four classes, which shade into one another. 

 a. Large oxeas, 7.5 mm. x 70 /a to 4 mm. x 35 /x, smooth, tapering. Many 

 are dilated in the middle region, and thus fusiform; others more cylindrical 

 in shape. Abundant in the parenchyma and roots ; smaller sizes in the 

 fringe round osculum. h. Very slender oxeas, 3-6 mm. long x 10-20 /a 

 thick ; cylindrical, tapering at both ends. Common in the parenchyma 

 and roots; chief spicule in the fringes round the osculum and pore areas. 

 c. Comparatively short and stout oxeas, 2-3 mm. long x 50-70 /a thick ; 

 fusiform. Common in the parenchyma, d. Small oxeas, 650 /x to 1.0 mm. 

 long X 8-10 /A thick ; common in the parenchyma, especially in the 

 peripheral region, where they project everywhere over the surface. 



Microscleres. 



5. Plesiaster. The spicule has a short, usually somewhat curved, axis 

 with 2 or 3 rays at each end, and sometimes with a ray or two projecting 

 from the axis. Forms with 4, 5, and 6 rays are all common, although the 

 4-rayed form is the predominant type. The rays are most minutely rough- 

 ened, scarcely spinose. Rays commonly 35-60 /x long with basal thickness 

 of 5-6 /u,. Smaller forms with ray length down to 20 jx occur. The plesi- 

 aster is very abundantly scattered throughout the parenchyma. 



Sollas for the "Challenger" specimens (Sollas, 1888, p. 72) gives the 

 plesiaster rays as 60-90 /x long x 3.9 /x thick. The rays in the specimens 

 studied are thicker and shorter. 



6. Spiraster. The spicule varies toward the metaster condition. The 

 common forms are shown in Plate 13, Fig. 3 a-c, among which 3 h and 



3 c approach the metaster type more closely than do the others. The 



axis is smooth and cylindrical, varies in length so as to exhibit in projection 



