GEODIA VARIOSPICULOSA. 61 



neck-like constriction, similar to the one at the cladomal end of the rhabdome, 

 is ol)served at the proximal end of the clades. In var. micraster the rhabdomes 

 of the orthoplagiotriaenes are 2.6-3 mm. long, and in the neck-like constriction 

 at the cladome 30-50 /i thick, their maximum thickness below this constriction 

 being 43-64 /<. The chords of their clades are 240-760 /^ long and enclose 

 angles of 99-105° with the axis of the rhabdome. In var. intermedia the 

 rhabdomes of these spicules are 2.4-3 nmi. long, and in the neck-like con- 

 striction at the cladome 35-65 // thick, their maximum thickness below this 

 constriction being 50-75 ft. The chords of the clades are 22&-550 ,« long and 

 enclose angles of 100-111° with the axis of the rhabdome. 



Besides these normal orthoplagiotriaenes, irregular forms are met with in 

 small numbers. In some of these one or two clades are bifurcate: these spicules 

 are transitional to the dichotriaenes. In others one or two of the clades are 

 cylindrical and not attenuated distally, or angularly recurved at the end. An 

 irregular triaene with one cylindrical and one terminally angularly recurved 

 clade is shown in Plate 17, fig. 46. In examining the rounded end of these ab- 

 normal cylindrical clades with the highest powers, I found the distal part of 

 the axial thread irregularly thickened at frequent intervals. At the end itself 

 the axial thread appeared split up into a bunch of very slender, thread-like, 

 divergent branches, which seemed to extend right up to the rounded, terminal 

 face of the clade. It seems that this terminal face is clothed with numerous 

 exceedingly small spines, and that one of the terminal branches of the axial 

 thread leads up to each of these spines. But as these structures are, in con- 

 sequence of their exceedingly small size, on the verge of visibihty, even with 

 the ultraviolet light (X = 280 /() employed, I could not make them out with 

 any degree of certainty. 



The dichotriaenes (Plate 17, figs. 38b, 48, 50), apart from the bifurcation of 

 the clades and the smaller size of the clade-rhabdome angles, are similar to the 

 orthoplagiotriaenes described above. In var. micrastei- their rhabdomes are 

 1.7-2.6 mm. long and in the neck-like constriction at the cladome 30-40 /< thick; 

 their maximum thickness is 45-58 fi. Their clade-rhabdome angles are little 

 over 90°. The clade-stems are 160-340 fi, the clade-branches 140-400 /< long. 

 In the preparations of var. int&-media no intact dichotriaene-rhabdomes were 

 found, so that their length is unknown. Their thickness is 45-48 /< at the 

 neck-like constriction at the cladome, and 55-60 // at the thickest point. 

 The clade-rhabdome angles are a little over 90°. The clade-stems are 150-160 ji, 

 the clade-branches 170-280 n long. 



