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L 



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114 



THE SPONGES. 



Microscleres. 



3. Microrhabd, Fig. 8 a-d, Plate 15. Spicule symmetrically curved, or 

 irregularly bent, sometimes nearly straight. Swollen in middle region, 

 tapering toward ends, which are not pointed but rounded. Exceptionally 

 a spicule, one of the smaller sizes, with pointed ends is found. A faint 

 annular ridge is frequently, but by no means always, visible in middle of 

 the spicule; ridge occasionally well developed. Abnormal spicules with 

 small lateral outgrowths near one end are of rather frequent occurrence. 

 Size, 160 /x x 8 /x to 60 /x x 5 /x. 



The spicule is thickly strewn in the superficial layer of the ectosome, 

 lying in the dermal membrane over the triaene cladomes as well as in the 

 pore areas. The spicule is also scattered in small number throughout the 

 ectosome and superficial part of choanosome (Fig. 9, Plate 15). 



4* Oxyaster, Fig. 10 a-c, Plate 15. Rays smooth, slender, conical, 

 about equal in size. Centrum small, but usually perceptible. When the 

 number of rays is large, they appear rather uniformly distributed around 

 the centrum. When they are less in number, it is easy to see that they 

 are not symmetrically distributed. The number of rays commonly varies 

 from about 10 to 20, the spicules with fewer rays being the larger. 



Diameter of spicule, 16-24 /x; centrum, 2-3 /x in diameter. 



Spicule 



present in some abundance in the walls of the canals, and rather sparsely 

 scattered throughout the parenchyma. 



5. Calthrops, Fig. 9, Plate 15. Rays about equal, 100-170 /x long, 

 smooth, tapering evenly from base to point. Such spicules are present in 

 small number, scattered in superficial part of choanosome. Possibly they 

 represent young stages of the triaenes. As is often the case with the 

 triaenes, the axial canal is abnormally wide, and is open at the ends of 

 the rays. 



Under the name of Stelletta pygmaeomm O. Schmidt (1880, p. 70, Taf. 

 IX, Fig. 9 a y b, c) has described a sponge from St. Vincent, 95 fathoms. 

 Sollas (1888, p. 203) assigns the species, with a query, to Ecionema Bwk. 

 Lendenfeld (1903, p. 67) records it among species dvMae. Schmidt's de- 

 scription, short as it is, indicates that the skeletal elements are very similar 

 to those of the species here described. 





