REPORT ON THE CALCAREA. 20 



the parenchyma by minute ones. These two characters are causally related to each other. 

 A thick cortex with a strongly developed spiculation, presenting a solid support for the 

 body of the Sponge, the parenchyma can extend itself on it like a crust, and the spicules of 

 the parenchyma becoming unnecessary, grow small. I think that when, as for instance, in 

 Leucetta clathria, H., the apical rays of the cortical quadriradiate spicules are strongly 

 developed, these apical rays possess rather a defensive than supporting function ; pro- 

 jecting from the inner surface their sharp ends present an armament protecting the inner 

 cavity ; and when such protection becomes useless, we see either that there are no quadri- 

 radiate spicules at all in the cortex (Leucetta corticata, H.), or very few, whose apical 

 rays remain far short of the inner surface (Leucetta hceckeliana, n. sp.). 

 The genus is represented by five species, namely : — 



Leucetta imperfecta, n. sp. 

 vera, n. sp. 



Leucetta hceckeliana, n. sp. 

 corticata, H. 



Leucetta clathria, H. 



Two have been described by Hseckel, three were collected by the Challenger. I 

 retain for the genus the name Leucetta, there being no doubt that the species de- 

 scribed by Hasckel under the generic name of Leucetta prior to his Leucetta corticata 

 all belong to the genus Leuconia. 



Pericharax, 1 n. gen. 



Leuconidse with distinct subdermal cavities. 



In vol. i. p. 237 of his Monograph, Prof. Hseckel states that the subdermal 

 cavities (intermarginal cavities of Bowerbank) are of rare occurrence in the Calcarea, and 

 that he met with them only in one case, namely, in his Leueandra cucumis. This is 

 quite true ; in most casus the inhalent canals in the same animal sometimes begin with a 

 dermal ddatation, sometimes, on the contrary, they are narrow near the outer surface, and 

 grow larger and broader in their centripetal course. Leueandra eucumis presents, 

 however, an exception. Here, according to Heeckel, one can speak of real, well-marked 

 subdermal cavities ; they are all on an average of the same dimensions, of the same form, 

 and even possess their own skeleton. The same I find in two specimens from Station 135 

 (Tristan da Cunha). In these forms the subdermal cavities, which are nothing but dilated 

 dermal parts of the inhalent canals (intercanals), are not so strongly developed as in 

 Leueandra cucumis, but are still quite distinct and also — at least in one specimen — 



1 From sr£g/, around, and x«e a l> palisade. 



