16 ART. ]. — T. T.TIM A : HEXACTTNELLTDA, III. 



shown ill figs. 5 and 0, came under my ol^servation. It seems 

 that through these forms tlie small hexactinose variety of hexasters 

 now in question passes over gradationally into the spherical 

 discohexaster next to be described. On the other hand, there 

 not infrequently occur, especially near the surface of the back 

 and of the gastral cavity, such forms as bridge over the gap 

 ])etween the present variety and the hexactinose codonhexaster 

 (fig. 8). The intermediate forms just referi-ed to are generally 

 somewhat larger than usual and possess terminal discs, which, by 

 elongation of the mai'ginal teeth, have acquired a moi*e or less 

 bell-like shape. 



The spherical discohexasters (PL IL, figs. 9-12) are large 

 and of great beauty, most closely resembling those tliat arc known 

 from Dictyaulus elegans F. E. Sen. I have found them only 

 close to the dermal layer on the back of the sponge, where they 

 occurred abundantly in some places (see fig. 14), but only occasional- 

 ly in others. They mostly measure 160-240 /^ in diameter. From 

 the expanded end of each short and stout principal there arise 

 in the smaller rosette 4 oi- ö terminals and in the larger ones 

 12 or thereabout. They are not always arranged in a whorl, 

 l)ut often one or more are seen to spring from a position inside 

 the points of origin of tlie peripheral ones. The slender terminals 

 thicken considerably at the outer end and are capped with a 

 strongly convex disc, which may measure up to 23 i^- in diameter. 

 Of the well developed marginal teeth tliei-e are 10-13, sometimes 

 more (up to 17), to a disc. All the terminal discs in a rosette 

 of the kind are approximately equidistant from one other, so 

 that a spherical form is given to the entire spicule. — Special 

 mention must be made of unusually small, normally developed, 

 ])ut onlv occasionally occurring discohexasters which seem to lead 



