150 THE SPONGES. 



and the same general arrangement of the canals. The skeleton too is 

 similar to that of /. lamella except in the matter of the bipocilli. 



The upper surface of a specimen is shown in Fig. 16, Plate 20, and 

 the lower surface of the same in Fig. 14, Plate 20. The efferent canals as 

 in the type pass into the body from both surfaces, sometimes passing 

 through from one surface to the other. As in the type the ujDper surface 

 is lighter in color, and bears more numerous oscula than the lower surface. 

 On the lower surface elongated vestibular spaces are extensively developed, 

 appearing as furrows lined with smooth membrane. The flagellated 

 chambers are of the same size as in the type. 



The two good specimens differ from the type as regards the detailed 

 appearance of the upper surface. The point is doubtless one of individual 

 difference, and in the remaining specimens could not be determined. In 

 these two specimens the upper surface bears abundant depressions, many 

 of which are furrow-like. The efferent canals open in the depressions 

 (Fig. 16, Plate 20). Here and there several efferent canals, instead of 

 opening separately, unite beneath the dermal membrane of this surface to 

 form a vestibular space, essentially similar to those which are more con- 

 spicuously developed on the lower surface. 



Skeleton. The megascleres, styles, and tylotes, are like those of the type, 

 and the skeletal arrangement offers no points of difference. 



Microscleres. 1. Bipocillus, 8-10 /x long, Plate 20, Fig. 15, a, c, d, 

 e, f. The curved axis terminates at one end in a thin plate-like expansion 

 having a spherical curvature and a rounded outline. This is usually 

 undivided, but occasionally spicules are found in which it is divided by 

 a deep median incision into two lobes, as in /. lamella. At the other 

 end the axis terminates in a smaller curved plate, which is pointed, and in 

 which the free edge on each side of the terminal point is minutely denticu- 

 late. Axis itself, near the larger end of the spicule, flattens out on each 

 side, forming a tliin lateral flange, which is separated from the terminal 

 plate by a rounded incision. The spicule is scantily present in the paren- 

 chyma, more abundant in the dermal membrane. 



2. Anisochela, 12-28 fx long, Plate 20. Fig. 15 ^. Spicule does not 

 differ from anisochela of the type, and is scantily present in the dermal 

 membrane and parenchyma. 



Comparative. The chelate character of the bipocillus makes a striking 

 point of resemblance between lophon lamella and lophon chclifcr R. and D. 



