THE SPONGES. 



149 



thicker in the middle, tapering toward each end. Heads small, minutely 

 spinose over distal half. Frequently one or two prickles on shaft, close 

 to ends. Precise character of end varies: end commonly enlarged and 

 rounded, but sometimes enlarged and irregular; sometimes not enlarged. 



Microscleres. 3. Bipocillus, 12-16 /x long, Fig. 7 a and c, Plate 20. 

 Curved axis shows a thickened median keel, which disappears toward 

 small end of spicule. On each side of keel, axis thins away, forming a 

 lateral flange which is sharply separated by a rounded incision from the 

 terminal plate. Axis terminates at one end, the larger, in a thin plate-like 

 expansion which has a spherical curvature, and is divided by a narrow 

 median incision into two lobes. At the other end axis terminates in two 

 pointed teeth, which project toward the larger end. 



4. Anisochela, 14-28 /x long, Fig. 7 b, Plate 20. The smaller sizes are 

 the commoner. Spicule of palmate type; a little spine at the smaller end. 



Skeletal Arrangement. Main skeleton a uniform reticulum of spinose 

 styles. Meshes are commonly triangular, but the shape may be construed 

 as due to the fact that a spicule or a small fascicle of spicules extends 

 obliquely across a squarish mesh, acting perhaps as a brace. Side of mesh 

 equal to length of a spicule and formed by 1, 2, 3 or occasionally more 



At the corners of the meshes the spicules are united by masses 

 of spongin, which is colorless. 



Dermal skeleton consists of the outermost layer of the skeletal reticulum, 

 and of scattered tylotes. The latter are frequently found in loose fascicles 

 or tracts, and occur throughout the dermal membrane. 



The microscleres are present in the dermal membrane, and in the paren- 

 chyma. They are very abundant in the walls of many of the canals. 



Iophon lamella indivisus, subsp. nov. 



Plate 20, Figs. 14-16. 



Diagnosis. Sponge distinguished from the type by the character of the bipocillus, 

 which is not chelate. Bipocillus, 8-10 /x long, terminating at the large end in a curved 

 plate of rounded outline, which is ordinarily not divided, terminating at the other end in 

 a smaller plate with denticulate margins. 



Station 3Jj05, 6 specimens. 



Along with the specimens of Iophon lamella were taken six other speci- 

 mens, four of which are fragmentary, having the same plate-like habitus 



