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PROCEEDINGS OF THE NATIONAL MUSEUM 



TOL. 81 



mic structures. With contraction of the sphincter these spicules are 

 tilted inward till their points almost or quite meet at an apex, cre- 

 ating a conical sliield or cap over the aperture. At the base of the 

 chamber there is typically a constriction, so that the opening from 

 it to the ramifying canals of the endosome is only about 100/* in 

 diameter. I have never observed the complete closure of the cap 

 above referred to, at the least an opening of 100/x being left, but it 

 may be assumed that upon appropriate stimulation, as perhaps by 

 attempted entrance of some enemy, complete closure would be 

 possible. 



Surface, superficially smooth, with projections as described above. 



Ectosomal specialization, spiculous; about lOOju, to '200fi thick of 

 spicules (principally the straight smooth subtylostyles) felted to- 

 gether exceedingly densely so there is room for but a minimum of 



PiGUEE 52. — Anaata sponijiyartina de Laubeiifels, X 300 



protoplasm. This makes an almost solid siliceous armor. From the 

 difficulty in tearing or cutting this layer, one may guess the presence 

 of spongin, but no evidence of it could be noted in sections. Endo- 

 some, a rather dense protoplasmic structure, with moderately numer- 

 ous acanthotylostyles, typically perpendicular to the substratum, 

 points upward. Histological details : There are flagellate chambers 

 up to nearly 50ja in diameter. 



Ectosomal spicules, subtylostyles (fig. 52, A) ; size, 6/* by 190/i, to 

 a/i by 210ju,. Endosomal spicules, acanthotylostyles (fig. 52, B, G) ; 

 size, 13/* by 115/a to 13/i, by 390/*. First microscleres, arcuate isochelas 

 (fig. 52, F) ; length, 42/t to 50/x. Second microscleres, arcuate iso- 

 chelas (fig. 52, E) ; length, 23/* to 25/*. 



Remarks. — The nearest relative of this species would seem to be 

 Leptosiopsis Topsent (1927, p. 13), type species Z. inaequalis. This 

 has anisochelas of the anchorate type and is much subject to deforma- 

 tion, thus separating that genus from Anaata decidedly. L. inae- 

 qualis has its ectospicules often polytylote and its endospicules 



