tn the Environs of Brussels. 391 



central cylinder surrounded by a tuberculous layer ; cylinder 

 circular or compressed (oval) in transverse section ; the 

 former ])rcscntin<^ on its surface a corrugated reticular linea- 

 tiun, whose interstices, clon*^ated transversely, arc, where most 

 regular, trapezoidal ; the latter, or compressed turm, lobed or 

 segmented longitudinally, and presenting a median linear 

 depression, extending from one end to the other, with similar 

 depressions at equal distances laterally extending outwards, 

 backwards, and downwards. Often branched. The whole 

 surrounded by a tuberculous structure whose surface is un- 

 equally ]>isiform, and whose crevices or intervals between the 

 pisitVirm projections reach down nearly to the central cylinder. 

 Pisiform tuljercles, where most regular, presenting the same 

 kind of trapezoidal arrangement as that seen on the surface of 

 the cylinder, only much exaggerated, with a tendency to sub- 

 division by inflection of the sides, through whieh the trapezoi- 

 dal form becomes more or less obliterated ; jjisiform tubercle 

 sometimes conical and extending outwards at right angles to 

 the cylinder laterally (fig. 2, /") ; the whole incrusted Avith a 

 layer of fossil sponge-spicules of different forms and belonging 

 to many different species, chiefly fragmentary and mixed up 

 with minute Foraminifera, the remains of minute Echinoder- 

 mata, cycloid Diatomacese, and quartz sand. Size variable, 

 about 20 centims. in length ; central cylinder variable below, 

 2 centims. in diameter ; tuberculous crust about a centimetre 

 thick towards the centre and upper part, less towards the tail. 

 Branched form equally invested by the tubercular structure, 

 which is prolonged upon the branches respectively. Com- 

 position varying with the situation, /. e. either entirely of 

 quartz sand, or calciferous quartz sand or argillaceous quartz 

 sand. 



Formation. Etage Bnixellicn or Mid-Eocene. 

 Locality. Environs of Brussels. 



Ohs. The presence of the sponge-spicules and other minute 

 organisms is, of course, contingent upon their presence in the 

 sea-bottom when the animal was growing. Thus in some 

 specimens, stated by j\[. Vanden Broeck to have come from a 

 fine sandy argillaceous deposit in the Lower Eocene ("' Sable 

 Ypri^sien (niveau du London Clay) h, Luttre") — which, from 

 their form, appear to me to be identical with the " tubula- 

 tions sableuses " of the t^tage Bruxellien or Mid-Eocene 

 about Brussels — there are no remains of spicules or any other 

 organism that I can see ; while the composition of the fossil, 

 being exactly that of the deposit in which it was imbed<lod, as 

 well here as in the quartz sand, seems to indicate that the 

 latter must have been composed of some soft and perishable 



27* 



