30 THE VOYAGE OF H.M.S. CHALLENGER. 



Sponge branched, with free cylindrical branches of equal thickness, each provided at 

 the distal end with an osculum. Pseudo-skeleton composed of Globigerina ooze. 



Ammosolenia rhizammina forms dendritic or branched tufts, composed of a variable 

 number of cylindrical, not anastomosing, branches. The small trees have a diameter of 

 8 to 12 mm., and are either erect or creeping on the bottom of the sea. The diameter 

 of the tubules is between 0"8 and 1"2 mm., the length between 10 and 16 mm. 

 Usually they are of nearly equal thickness, and open at the distal end by a circular 

 mouth. The thin wall of the tubes seems to be solid, and to consist only of Globigerina 

 shells cemented together by a scanty maltha. But after removal of the calcareous matter 

 by hydrochloric acid, and staining the residuum by carmine, there remains a thin 

 membrane pierced by numerous small pores. These are disposed in the same manner as 

 in Ammolynthus haliphysema (PI. VIII. fig. 2) and in Ammoconia auloplegma (fig. 4). 

 Between the pores are visible here and there small cellular flakes, composed of minute 

 granular cells, perhaps the remnants of the flagello-epithelium. A careful examination 

 of living and well-preserved specimens is, however, required to confirm the sponge-nature 

 of this as well as of the other Ammoconida3 with certainty. 



Genus 3. Ammoconia, 1 n. gen. 



Definition. — Ammoconidse of reticular shape, forming a network of anastomosing 

 porous tubules, without oscula. 



The genus Ammoconia among the Keratosa represents the same characteristic 

 form, which is very common among the calcareous Asconidae, described in my 

 Monograph (1872) as Auloplegma. The sponge consists of a network, composed of 

 numerous thin-walled (usually cylindrical) anastomosing tubes. The thin walls are 

 pierced by numerous small round pores, but there is no larger opening or osculum. 

 Whilst the thin outer wall of the tubes in Auloplegma is supported by calcareous 

 spicules formed by the sponge itself, in Ammoconia it is built up of xenophya, or 

 foreign bodies taken from the sea-bottom. There are two similar species of this genus 

 found on the sea-bottom ; in the first [Ammoconia auloplegma) the pseudo-skeleton is 

 formed by calcareous Globigerina ooze (PL VIII. fig. 4); in the second {Ammoconia 

 sagenella) it is sandy and siliceous, composed of sponge spicules and the volcanic debris 

 of the red clay. Very similar to this latter, or even identical with it, may be that 

 form which Brady has figured as Sagenella frondescens. 2 



1 Ammoconia = Sandy cement, dfiftox-oviee. 



- Zool. Chall. Exp., pt. xxii. p. 278, pi. xxviii. figs. 14, 15. 



