CALCAREOUS SPONGES. 767 



Genus 33. Sycyssa Haeckel [1872]. 



Diagnosis. Canal system syconoid. Skeleton entirely composed 

 of oxea. Dermal cortex well developed, but without colossal 

 longitudinal oxea. Gastral cortex with a subgastral layer of 

 oxea, arranged longitudinally. 



For illustrations of this genus see Haeckel [1872]. 



This genus is highly remarkable for the complete suppression 

 of the radiate spicviles. An analogous condition is met with in 

 Ascyssa. Leucyssa, Trichogypsia and Kiiarrhaphis . 



The only known species is : — 



1. S. HUXLEYi Haeckel. 



Sycyssa huxleyi Haeckel [1872]. 



Genus 34. Megapogon Jenkin [1908 B] (emend.). 



Diagnosis. Canal system sylleibid or leuconoid. Skeleton of the 

 chamber layer retaining clear traces of the original articulate 

 character and not confused ; composed chiefly of subgastral 

 sagittal quadriradiates, with their apical rays projecting into 

 the gastral cavity ; with a few sagittal triradiates arranged 

 as usual. N'o gastral skeleton of tangentially placed radiates, 

 except round the osculum. No colossal longitudinal oxea. 



For illustrations of this genus see Jenkin [1908 B]. 



Jenkin included in this genus five species, M. cmciferus^ 

 M. villostbs, M. raripilus, M. pollicarls and M. crispatus, and 

 placed it in the family Staurorrhaphidfe on account of the 

 presence of so-called chiactines. His figure of M. villosus, 

 however, is alone sufiicient to indicate that the "chiactines" 

 are merely subgastral sagittal radiates which have developed 

 apical rays, as in so many other cases, and we find it necessary 

 to base the genus, which we believe to be a natural one, on other 

 characters. 



The absence of tangentially arranged gastral radiates, combined 

 with the presence of the so-called " chiactines," might be used as 

 an argument for the validity of the chiact theory, on the sup- 

 position that all the gastral tangential radiates had been converted 

 into chiactines, but we must remember that in one species at any 

 rate, M. rarijnlus, the so-called chiactines are associated with 

 subgastral sagittal triradiates, which differ from them only in 

 the absence of an apical ray, and there is no ground for supposing 

 that the chiactines have any special significance. It is quite 

 possible that all these subgastral sagittal spicules have been 

 rotated into their present positions, as already pointed out in the 

 Introduction, but this fact does not justify us in distinguishing 



