PLACOSOMA PARADICTYUM. 17 



the large spherical diseohexaster gradationally over to the small 

 hexactinose diseohexaster l)efore described, especially to the 

 hemihexasterous form of this rosette. We have here to do with 

 spherical discohexasters of under 150/^- diameter, leading doAvii to 

 100/^- or less (even to 'jö/<). Fig. 9, PI. II., represents one such 

 case, measuring about 100 /' in diameter. Two or three, some- 

 times four, terminals belong to a principal ; the terminal disc 

 is just the same as in a small hexactinose diseohexuster. — 

 Xotewortliv also seem the cases — quite rare though these are — of 

 certain moderately large (132/^ diameter) discohexasters in which 

 4 or Ü terminals, each ending in a bell-shaped terminal disc, belong- 

 to each principal (see fig. 10). Here is apparently an approach 

 of the normal discohexasters to the hexactinose codonhexaster next 

 to be described ; but an intermediate hemihexasterous codonhex- 

 aster has not been met -with. 



The hexactinose codonhexcisters (PI. IL, figs. 11, IG) occur 

 in great abundance just under the gastral layer. The powdery 

 appearance, before noticed, of that layer is due to their crowded 

 presence. They are also found in the parenchyma generally, 

 but only quite seldom and at Avide intervals. Diameter in 

 most cases 110-176 !'. The slender hexradiate rays, arising 

 from a small central node, are usually more or less bent. 

 Here again the axial filament of the central cross extends, as 

 a matter of fact, only a very short distance into the base of the 

 ra^'S. The deeply bell-like terminal umbel may be 30 !'■ broad 

 and 42/-« long; the long teeth of the sides 12-16 in lUTmber. 

 I have already indicated that this category of the hexasters is 

 connected with the small hexactinose discohexasters by forms that 

 are intermediate both in point of size and of the shape of the 

 terminal disc. 



