GEODIA VARIOSPICULOSA. 



63 



position, in which one, two, or all three clades are stunted, short, and rounded 

 at the end; 3, anatriaenes of normal dimensions with two simple and one bifur- 

 cate clade; and 4, anatriaene-derivates of normal dimensions, in which one of 

 the clades is directed upward, proclade-fashion. (1) is very, and (2) fairly 

 abundant in both varieties; (3) and (4) are very rare and have been found 

 only in var. intermedia. In the small anatriaenes with pointed clades (Plate 

 17, figs. 23, 28) the rhabdome is only 12-20 /x thick at the cladome, the clades 

 being 30-50 /< long in var. intermedia, and 30-65 n long in var. micraster. Of 

 course these anatriaenes may be young forms of the normal ones. Their 

 abundance on and close to the surface, however, renders this assumption some- 

 what doubtful. The anatriaenes with stunted clades (Plate 17, fig. 31) exhibit 

 very different degrees of clade-reduction. In most of them only one or two 

 clades are shortened and rounded; in some, however, one or two clades are 

 reduced to low, rounded protuberances and the others (other) shortened to half 

 or less than half of the normal length. These extreme forms have been met 

 with chiefly in var. intermedia. In the few anatriaenes with one bifurcate clade 

 the two other (simple) clades were more or less stunted. In the anatriaene- 

 derivates with one clade directed upwards the clades are pointed, but much 

 shorter than in the normal anatriaenes. 



The minute dermal anaclodes (Plate 18, fig. 24a; Plate 19, figs. 3, 6-10, 14) 

 are mostly anatriaenes with well-developed clades. A few of them have, how- 

 ever, by a more or less complete clade-reduction become anadiaenes, anamo- 

 naenes (Plate 19, fig. 6), or even tylostyles. These latter are, however, very 

 rare. The rhabdome is more or less curved, simply or in an S-shaped man- 

 ner, and thickest at a point from a fifth to a third of its length above its acla- 

 domal end. From this thickest point it is gradually attenuated towards both 

 ends. The acladomal end is rounded. The thickness of the two ends of the rhabd- 

 ome is from 25-60 % of its maximum thickness. In many of these spicules a 

 slight local thickening of the rhabdome, situated nearer the acladomal than the 

 cladomal end, similar and probably analogous to the local thickening of the 

 small dermal styles, has been observed. The apex of the cladome is simply 

 rounded off or crowned by a protuberance (Plate 19, fig. 9). In var. micraster 

 the minute anaclades without apical protuberance greatly predominate, in var. 

 intermedia a much greater proportion of them possess such a protuberance. 

 The clades are conic, sharp pointed, strongly recurved in their basal part, and 

 nearly straight in their terminal part (Plate 19, figs. 3, 14). In var. micraster 

 the rhabdomes of the anaclades are 275-410 /< long, 1.5-4 n thick at the 



