214 



GEODINELLA ROBUSTA. 



ends. In a few one end was intact and pointed. Their slenderness would 

 incline me to believe that they are parts of rhabdomes of teloclades, but the fact 

 that, in spite of the most careful search, I have failed to find any cladomes 

 belonging to them, is against this view. As stated above, these spicules may 

 be foreign to the sponge. 



The large oxyasters and small oxysphaerasters (Plate 2, figs. 3a, 10a, b; Plate 

 4, figs. 1-5, 21, 22) are so closely connected by transitional forms that it is 

 advisable to describe them together. In var. carolae these spicules are 11-36 pt 

 in diameter and have from six to eighteen rays. In many a central thicken- 

 ing 2-8 /I in diameter is clearly distinguishable, others are without such a 

 centrum. The rays are straight, conic, 1-3.5 fi thick at the base, and (without 

 the central thickening) 3-17 pt long. They are usually simple, but occasion- 

 ally such asters are observed in which one or more of the rays are bifurcate, 

 the two branches extending in a nearly parallel direction and lying close 

 together. The rays are pointed (Plate 4, fig. 3) or, rarely, somewhat blunt (Plate 

 4, fig. 2). Their distal part is covered with spines, the size, number, and 

 arrangement of which are variable. In some (Plate 4, fig. 2) the spines are 

 so small that even with the 280 pfi light no distinct image of them can be pro- 

 cured; as a rule, however, they are large enough to be clearly shadowed on the 

 photographic plate by these u. v. rays (Plate 4, fig. 3). The number of rays 

 and the development of the central thickening are, roughly speaking, in inverse 

 proportion to the size of the spicule. Oxyasters (oxysphaerasters) under 20 fx 

 in diameter have from ten to eighteen rays and a well-developed central thick- 

 ening, the diameter of which is from one fifth to nearly one half of the diameter 

 of the whole spicule. Oxyasters (oxysphaerasters) over 20 /i in diameter usually 

 have only from six to nine rays, and either no central thickening at all, or only a 

 small one, never more than a quarter of the whole spicule in size. Also in the 

 spines a certain (inverse) proportion between size and number is discernible; 

 when the spines are numerous, they are very small, and the smaller their num- 

 ber is the larger they become. When, as is most frequently the case, the spines 

 are few in number and large in size, some, generally the longest, form a verticil a 

 little below the end of the ray, so that the spicule becomes somewhat acanthtyl- 

 aster in character (Plate 4, fig. 3). The oxyasters and oxysphaerasters of var. 

 megasterra are similar to those of var. carolae. They measure 9-38 p in diameter 

 and have from six to seventeen rays (without the central thickening) 2.5-21 /i 

 long, and 0.6-4 fi thick at the base. The central thickening is small, never over 

 5 /X in diameter. In many of these spicules (Plate i, fig. 4) the spines of the rays 



