in the Environs of Brussels. 383 



apecimens also of the sand from the deposit {'^Gr<is lustrh^'') 

 in which they are vertically imbedded. (According to ^I. Rutot, 

 op. ci't., the " Bruxcllicn etage " consists, from below up- 

 wards, of: — 1, cuMglomerat siliccux ; 2, grcjs lustrds ; 3, gres 

 calcarif (ires ; 4, couche roulee h Xummu/ites la;vif/ata.) And 

 although the specimens are all, with the exception of one (which 

 is witliout the " concretionary crust," to be hereafter men- 

 tioned), more or less fragmentary, still there is quite enough 

 for me to give the following description of them, which seems 

 to indicate the kind of organism of which they are now alone 

 the fossil representatives. 



As a preliminary measure, it is desirable to premise a 

 description of the exterior (since I do not like to destroy the 

 fossil by breaking it open) of that exceptional specimen which 

 appears to me to be almost ])erfect (PI. XVIII. fig. 1). It is 

 cylindrical in form, a little more than 18 centims. long by 3 

 centims. broad in its greatest diameter, which is the middle 

 of the lower half (I shall assume henceforth that the pointed 

 extremity is the lower or posterior portion), slightly sigmoid, 

 and unequally pisiform-tuberculous on the surface throughout 

 except at the extremities (fig. 1, a a a). The upper half or 

 9 centims. has much the same diameter throughout, viz. 3 

 centims., ending in a truncated extremity above, which shows 

 that the tuberculous surface is the outer part of a layer formed 

 upon a solid central cylinder 1^ centim. in diameter (fig. l,b); 

 while the lower half becomes gradually inflated towards its 

 centre, which, as above stated, is 3 centims. in diameter, after 

 wdiich it diminishes rather rapidly to a point that is not in the 

 line of the vertical axis, but turned to one side of it, and cha- 

 racterized on one half by a smooth, ?/«tubcrculated, somewhat 

 spiral depression, which ends in the point (fig. 1, c). Thus 

 constituted, the whole presents a slightly sigmoid cylinder 

 truncated at the upper, and pointed at the lower end, of equal 

 size througliout the upper half, and inflated towards the 

 centre in the lower one, with a generally unequal, pisiform- 

 tuberculous surface. In composition it consists of sand- 

 grains (quartzitc) held together by a white calcareous clialky 

 cement ; so that this specimen might have originally come 

 from the upper part of the strata alluded to in M. Kutot'a 

 paper (p. 4 of the separate copy). 



We will divide the " tubulation sableuse " as 31. Rutot 

 has done, into three portions, which I would term, respec- 

 tively, the central cylinder, the tuberculous layer, and the 

 concretionary crust — the two former being proper to the 

 fossil, and the latter derived from the deposit in which it is 

 imbedded. 



