CALCAREOUS SPONGES. 757 



the Calcarea. We have seen it ah-early, for example, in Leitcetta, 

 Leucaltis and Leucettusa^ and liave not in those cases considered 

 the presence of such spicules as of generic value. In Grantilla, 

 however, they seem to assume more importance, and to take a 

 larger share in the formation of the skeleton of the chamber layer. 

 Nevertheless, had the genus not been already in existence, we 

 should have hesitated to propose it on this character alone. 



The only known species of the genus is : — 



1. G. QUADRIRADIATA RoiU. 



Grantilla quadriradiata Row [1909]. 



Family 8. GRANTIID^ Dendy [1892] (emend.). 



Diagnosis. With a distinct dermal cortex and a proper cortical 

 skeleton of tangential radiates, sometimes supplemented by, 

 and occasionally replaced by, oxea. Flagellate chambers 

 ranging from elongated and radially arranged to small, 

 spherical and irregularly scattered. Skeleton of the chamber 

 layer ranging from regularly articulate to irregularly 

 scattered. Typically with subgastral sagittal radiates. No 

 subdermal pseudosagittal triradiates. Subdermal quadri- 

 radiates, if present, always associated with a chamber-layer 

 skeleton containing confused triradiates. Nuclei of collared 

 cells probably always apical. 



It must frankly be admitted that the boundary line between 

 the Sycettidce and the Grantiidje is by no means shai-ply defined. 

 The great distinguishing feature is the presence in the latter of a 

 distinct dermal cortex with its own proper skeleton. The develop- 

 ment of such a cortex appears to have formed the determining- 

 condition for the farther evolution of both the canal system and 

 the skeleton, and it must therefore be regai'ded as of great system- 

 atic importance. 



The first commencement of such a cortex is, however, so slight 

 as to be almost indistinguishable from the mere pore-bearing 

 dermal membrane of the most highly specialised Sycons. In 

 Grantia compressa the cortex is so feebly developed that Dendy, in 

 his early work [1892 B], included this species in the genus /St/con, 

 laying more stress upon the presence of dermal tufts of oxea than 

 we are now inclined to do in this connection. It appears to us 

 that the line between Sycon and Grantia, and therefore between 

 the Sycettidfe and Grantiidge, must be drawn at the appearance 

 of a dermal cortical skeleton of tangentia,! radiates distinct from 

 the skeleton of the radial chambers, and in accordance with these 

 views Grantia compressa is excluded from the genus Sycon. 

 Moreover, it must be pointed out that G. compressa is not the 

 only member of this family in which dermal tufts of oxea occui-, 

 as they are present also in Sycute dendyi Kirk. 



50* 



