760 MR. A. G. THACKER ON [J Vine 16, 



but the largest of the three specimens is not more than one-sixth 

 the size of that figured by him. The sponge is composed of a 

 compact reticulum of Ascon-tubes, but there is no common in- 

 vesting skin or pseudoderm covering the whole colony and no 

 endogastral network. 



Colour (in alcohol) pale brown. 



The Skeleton, which consists of all three kinds of spicules, shows 

 only slight differences from Haeckel's description (text-fig. 155). 



The triradiates are regular and fairly sharply pointed ; they 

 vary in length from 0"12 mm. to 0'18 mm, and in basal width 

 from 0-011 mm, to 0*016 mm. The quadriradiates are less nume- 

 rous than the triradiates and difier from them only by the presence 

 of the fourth ray, which is the same length as the facial rays but 

 only a little more than half as thick and is straight and sharply 

 pointed. The oxeote spicules are somewhat smaller than those 

 described by Haeckel ; they vary in length from 0'35 mm. to 

 0*55 mm. and in maximum width from 0-025 mm. to 0-035 mm. 

 They are either quite straight or very slightly curved and are 

 sharply pointed, especially at one end. A few extremely fine 

 hair-like oxea occur in my specimens ; their presence is not to be 

 regarded as of much systematic importance. 



Distribution. Atlantic coast of North America; Florida (^aec^e? 

 [14]); CapeYerde Islands (Crossland Collection). 



Leucosolenia atlantica, sp. n. (Plate XL. fig. 2 & text-fig. 

 156.) 



The collection contains two specimens of this species, both 

 dredged from a depth of 20 fathoms off North Point, Boa Vista 

 Island. The sponge is composed of large Ascon-tubes which for 

 the most part are much separated from each other, but which 

 occasionally fuse together into a larger mass and then separate 

 from each other again (Plate XL. fig. 2). There is of course no 

 pseudoderm uniting the whole colony, and there is no endogasti-al 

 network. The diameter of the Ascon-tubes varies from 0-8 mm. 

 to 1-2 mm. and the thickness of the wall is 0-2 mm. The oscula 

 have a diameter of about 0-7 mm. The colour (in alcohol) is 

 straw-yellow. 



The Skeleton consists of middle-sized triradiates, of middle-sized 

 quadriradiates, of large quadriradiates, and of oxeotes (text-fig. 156). 



The triradiates are regular and have cylindrical, rathei' sharply 

 pointed rays. The average size is : length 0-12 mm,, width of 

 rays at base O'Ol mm. These spicules do not vary much in size 

 and are distributed without order in the thickness of the body- 

 wall. 



The middle-sized quadriradiates resemble the triradiates except 

 for the presence of the fourth ray. The apical rays are feebly 

 developed on these spicules, being thinner than the facial rays 

 and not more than one quarter as long. 



