E. IMPERIALIS. OEN. CHARACTERS. 63 



The parictnJ ledger or pi-oiicberanc.ef< are very well developed 

 and constitute a very characteristic feature of the species. They 

 may in general Ite described as irregular ridges which are sub- 

 ject to frequent interruptions in tlieir course and which, far 

 from presenting even surfaces and edge-lines, are cut up into 

 numerous tubercular, knob-like or flap-like protuberances that 

 lend a peculiarly corrugated or jagged appearance to the sponge. 

 In this respect the present species presents a striking contrast 

 to its nearest allies, £. aapergiUuni and E. regalh. 



At places the nappy ledges arc seen running, numbers of 

 them together, in an oblique direction, one way or the other, 

 or in two intersecting oblique systems ; in other places they may 

 show an altogether irregular disposition, often bending, branching 

 or anastomosing in their course. They are certainly less con- 

 spicuously developed in young than in old specimens. In the 

 former there exists immediately below the cuff a narrow zone in 

 which the ledges are scarcely or not at all developed (PL II, 

 figs. 4, 6, 7) ; in the latter these may extend right up to, and 

 join the base of, the cull' on its underside (PI. I, fig. 1). Towards 

 the lower extremity, the body is usually denuded to a greater 

 or less extent of its peripheral loose tissues and with these the 

 ledges also (figs. 1-3), thus exposing the bundles of basal spicules 

 apposed to the skeletal latticework. So far as the prominences 

 occur on the parietes, they are either tolerably uniformly devel- 

 oped all over the body or may show greatest development in 

 the middle region. In the largest individual before me (spec. 

 L of the appended table) some of them measure as much as 14 

 mm. in height above the level of the parietal oscula. 



Certain flat lappets of the parietal ledge, particularly those 

 with a sharper edge, are distinguished from the rest by having 



