738 PROB'. A. BENDY AND MR. E. W. H, ROW ON 



We recognise only the following species in the genus : — 



1. L. CLATHRiA Eaeckel. 



Leucaltis clathria Haeckel [1872]. 



Hetero'peg'ma nodus-gordii Polejaeff [1883], Jide Dendy 



[1913]. 

 Glathrina latitubulata Carter [1885-1886], Jide Dendy 



[1913]. 

 Leucaltis bathybia var. mascarenica Ridley [1884], Jide 



Dendy [1913]. 

 Leiocaltis clathria Dendy [1913]. 



Genus 10. Leuoettusa Haeckel [1872] (emend.). 



Leucetta Polejaeff [1883]. 



Diagnosis. Sponge colony individualised, with definite external 

 form and large central cavity opening by a large single 

 osculum. Canal system leuconoid. 



For illustrations of this genus see Polejaeff [1883] under the 

 name Leucetta, and Row [1913 MS.]. 



The remarkable reticulate type of colony formation found in 

 Leucaltis prevents us from regarding that genus as directly 

 ancesti'al to L&ucettibsa, but as regards canal system the two are 

 related in the same way as Grantia and Leihcandra. 



Within the limits of the genus Leucettusa, however, we find 

 considerable variation with regard to the form of the flagellate 

 chambers. Polejaeft''s figure of the canal system of Leucettusa 

 {Leucetta) vera shows the flagellate chambers in the outer part of 

 the chamber layer elongated and radially aiTanged, while those 

 in the inner part are subspherical and scattered, so that this 

 species appears to be intermediate between Leucaltis and the 

 more typical Leucettusas in this respect. 



Leiicetticsa (Leucetta) haeckeliana, on the other hand, has the 

 flagellate chambers all small and subspherical, and lying in the 

 irregular trabeculse of the chambei- layer, which are separated by 

 very wide, irregular exhalant lacunae. In Leucettusa dictyogaster 

 Row [1913 MS.] the trabeculae bearing the flagellate chambers 

 form a network which almost completely blocks up the central 

 gastral cavity as an altogether askeletal layer. A section of this 

 askeletal chamber layer, isolated from the cortex, would be almost 

 indistinguishable from a similar section of Oscarella, which also 

 has large collared cells with basally placed nuclei, so that the 

 possibility presents itself that Oscarella may be nothing but a 

 calcareous sponge which has lost the whole of its skeleton. 



We also find in the genus Leucettusa various stages in the 

 development of the subdermal quadriradiate spicules, which are 

 entiiely absent in L. cot^ticata and L. dictyogaster, very sparse 

 in L. haeckeliana and large and very numerous in L. vera. As 



