TLACOSOMA rARADICTYFM. 15 



l)ack. Length (»f tlie longest — the radially directed — axis, 600- 

 800 ,«. Paratangentials 200-260 ,« long. The free gastral ray is 

 of abont the same length, or shorter ; it is not always rounded 

 at the end, but may be gradually tapering and conically pointed 

 like the other rays. Thickness of rays near base 73-8 /^ 



The hexasters of the species l^elong all to one type, the 

 discohexaster ; but this occurs in no less than three varieties 

 of markedly different characterization, viz., the hexactinose 

 discohexaster, the spherical discohexaster and the hexactinose 

 codonhexaster. Floricomes and graphiocomes are not present. 



Bv far the most abundant and the most «ienerallv distributed 

 are the small hexactinose d hcoliexasters (PI. II., figs. 4 and 7). 

 They are very numerous about the hypodermal beams of the 

 frontal lattice and everywhere in the parenchyma (see figs. 13- 

 16). The manner of their distribution in large numbers reminds 

 one of that of micramphidiscs in certain Amphidiseophora. The 

 size is subject to considerable variation. In most cases the 

 diameter measures 30-60 !'-, on an average about 46 !'■ ; but oc- 

 casionally, and especially near the l)ack surface of the sponge, 

 the hexaster attains a much larger size, reaching 100 /-« in diameter. 

 The axial filaments in the central node extend, as determined by 

 direct observation, only to the base of the six moderately strong 

 rays. Tlie watchglass-like or nearly hemisj^herical terminal disc 

 measures 8-15 !>- across ; its well developed marginal teeth vary 

 from 8 to 15 in number, according to the smaller or larger size 

 of the spicule. In some rare instances I have found the terminal 

 disc unusually small and toothless, a condition which is probably 

 to be considered as representing a stage in its developmental 

 history. Also a few cases of heraihexasterous forms, such as are 



