CALCAEEOUS SPONGES, 737 



Genus 9. Leucaltis Haeckel [1872] (emend.). 



HeteropegTna Polejaefi' [1883]. 



Diagnosis. Sponge colony tubular, ramified and anastomosing, 

 with many oscula. Flagellate chambers elongated and 

 branched, more or less radially arranged round the central 

 gastral cavities of the tubes. 



For illustrations of this genus see Polejaeff [1883] and Dendy 

 [1893 A]. 



Dendy [1892 B, 1893 A] placed this genus in the family Am- 

 phoriscidse, on account of the large subdermal quadrii^adiates 

 possessed by the only known species. He also regarded the 

 vestigial triradiates of the skeleton of the chamber layer as the 

 remnants of an articulate tubar skeleton, being misled by the 

 radial arrangement of the flagellate chambers. We are now 

 convinced that in both these respects he was wrong, and that 

 the genus is probably, as Bidder [1898] maintained, related 

 to Dendya, from which it has been directly derived without 

 passing through an intermediate syconoid stage. 



In arriving at this conclusion we lay great sti-ess vipon the 

 regular and equiangular form of the triradiates of both the 

 chamber layei- and the dermal cortex, and also upon the basal 

 position of tlie nuclei of the collared cells. The genus may, in 

 fact, almost be regarded as a Dendya with a thick dermal cortex. 



Dendy [1913] has shown that only one species can be re- 

 cognised in the genus. A re-investigation of the type specimen 

 of Haeckel's Leucaltis clathria has convinced us that it is not 

 only generically, but also specifically identical with Polejaeff's 

 Heterojiegma nodus-gordii, and the latter name thus becomes a 

 synonym of Leucaltis clathria Haeckel. As the other species of 

 Haeckel's genus Leucaltis must be removed to older genera, 

 L. clathria must be taken as the typical species, and we are 

 therefore unable to retain Polejaeff's name Heteropegtna. Again, 

 Carter's Clathrina latituhulata is only a vaiiety of Leucaltis 

 clathria, diftering in some slight details of spiculation. Mr, 

 Carter seems to have been led into provisionally placing his 

 species in the genus Clathrina by the external foi'm of the whole 

 colony, which resembles a reticulate Clathrina on a gigantic 

 scale. The reticulation, however, is not composed of simple 

 ascon tubes as in Clathrina, but of a colony of a higher order, 

 with numerous true ascon tubes lying in the thickness of the 

 wall. Finally, Ridley's Leucaltis hathyhia var, mascarenica is 

 evidently, from his description, and from the slides which we 

 have been able to examine, nothing but the same species. 



The extent to which apical rays are developed on the tangential 

 radiates of the dermal cortex varies greatly in different in- 

 dividuals. 



