180 



GEODIA AMPHISTRONGYLA. 



dimensions. The rays are cylindrical or slightly thickened distally and have a 

 flat or convex terminal face from which a bunch of stout spines arises. The spines 

 forming this launch are sometimes nearly parallel to each other and to the axis 

 of the ray, sometimes they diverge, occasionally so much so that the outermost 

 ones become nearly vertical to the axis of the ray. Generally the sides of the 

 rays are quite smooth. Sometimes, however, I have observed small spines on 

 them. The rays are 1-2 p. long and 0.8-1.8 n, usually about 1 p. thick. The total 

 diameter of the strongylosphaerasters is 4.8-8 p., usually 5-6.5 p. The strongylo- 

 sphaerasters with numerous rays are on the whole smaller than those with few 

 rays. Thus those with ten or more rays measured were 4.8-6.5 p, those with 

 from seven to nine rays 6-8 p, in diameter. 



Besides these normal strongylosphaerasters I found a few sphaerasters 

 similar in size, with much more numerous (from fourteen to nineteen) and more 

 slender, conical rays. Perhajjs these were foreign, or — which, however, does not 

 seem very probable — young forms of the oxysphaer asters. 



The sterrasters (Plate 20, figs. 9, 28d, 30d, 32, 37, 38, 40, 41) are flattened 

 ellipsoids and measure 100-110 p in length, 87-94 p in breadth, and 72-78 p 

 in thickness. The average proportion of length to breadth and to thickness is 

 100 : 87 : 74. The young forms, which are very abundant in the choanosome, 

 are enclosed in endothelial capsules (Plate 20, fig. 9) and composed, as usual, of 

 slender rays the proximal parts of which coalesce to form a solid mass (Plate 

 20, figs. 9, 28d, 30d). In the centre of this a few irregularly distributed granules 

 are observed. The distal parts of the rays projecting freely over the surface of 

 the adult sterrasters (Plate 20, figs. 37, 38, 40, 41) are everywhere, except close 

 to the umbilicus, 3-3.5 p thick and provided with terminal verticils of from 

 three to five stout, conical, and straight lateral spines, 1.5-2 p long and at the 

 base 1.5 p thick. The rays surrounding the umbilicus have a transverse sec- 

 tion, elongated in a direction radial to the centre of the umbilicus, which meas- 

 ures 3-3.5 p in breadth and 4-4.5 p in length. These rays are provided with a 

 greater number, some with as many as nine, terminal, lateral spines. The 

 spines of these rays pointing inwards, towards the umbilicus, are larger than the 

 others, up to 2.5 p long, and more or less curved. 



This sponge was collected on the shore at Easter Island on December 

 20, 1904. 



On account of its cribriform pores and its spiculation this sponge must be 

 placed in Geodia. I have compared it with the known species of Geodia and of 

 Sidonops. The only species of these genera with similar sterrasters, in which 



