1908.] CAPE VERDE ISLANDS SPONGES. 775 



(text-fig. 164, c). These are sagittal and resemble those 

 described by Polejaeff. Lateral rays 0*35 mm. long, basal ray 

 0'2 mm. long ; apical ray varies in length from 0*05 to 0"12 mm., 

 usually slightly curved. All rays of the same basal diameter, 

 O'OIS mm. There ai"e a few triradiates in the gastral cortex ; 

 these only differ from the quadriradiates by the absence of the 

 apical ray. As in the case of PolejaelFs specimens, these quadri- 

 radiates also occur in small numbers in the walls of the exhalent 

 canals. 



Some large oxeote spicules are scattered about in the paren- 

 chyma ; the greatest thickness of these is 0*055 mm. and they 

 reach a maximum length of 2 mm., but usually do not exceed 

 1"5 mm. Many of these spicules do not project beyond the dermal 

 cortex at all, and over the greater part of the surface of the sponge 

 they never have more than one-third of their length projecting ; 

 near the osculum, however, they extend much further beyond the 

 surface. The spicules are spindle-shaped and sharply pointed at 

 both ends (text-fig. 164, d). They are not numerous. 



There are also some very small oxea ; these ai-e either straight 

 or slightly curved, and are fairly sharply pointed at both ends. 

 They are shorter than those described by Polejaefli" ; I found none 

 longer than 0*25 mm, and they are usually only 0*15 mm. long. 

 Their thickness is 0"003 mm. They occur either singly or in 

 small bundles in or just beneath the dermal cortex, beyond which 

 they often project. They are not numerous. 



The minute and very peculiai- spined grapnel-like oxea (text- 

 fig. 164, f) of the gastral cortex form the main specific character of 

 this Leucon. It is these spicules which Polejaefi" describes as 

 " vei'ticillate " oxea, but this term does not appear to be quite 

 accura.te, for the spines are not really arranged in verticils, but 

 project on each side of the spicule alternately down the length of 

 the shaft. These oxea reach a length of 0'06 mm. and their 

 thickness varies fi-om 0*0007 to 0*0011 mm. They are sometimes 

 quite straight and sometimes curved throughout their length, but 

 usually the spicule is straight in its distal and bent in its proximal 

 part, which also seems to be slightly flattened and is slightly 

 wider than the distal half, but I have not found any spicules so 

 much expanded in this region as that figured by Polejaefi" in 

 plate vii, fig, 3 a, iii, [19]. In a few of the spicules the spiked 

 head is much reduced, these spicules being evidently intermediate 

 between those with large heads and ordinary spindle-shaped oxea. 



Two of the specimens possess oscular fringes composed of 

 spicules of the usual form — long, very fine oxea of maximimi 

 length 1*3 mm. and width 0-0025 mm. There is of coui^se 

 nothing remarkable in the presence of oscular fringes in two of 

 the specimens and its absence in the third, for there are many 

 Calcarea in which this structure is indiff'erently present or absent. 



There is a peristome, and this structure is best developed on the 

 specimen without an oscular fringe. It is composed of a complex 

 network of spicules of all those types which occur in other regions 

 of the body — lai-ge triradiates, small triradiates, small sagittal 



