in the Environs of Brussels. 389 



Kiitzingiana^ which, according to Smith (Synop. Brit. Diatom, 

 vol. i. p. 27, pi. V. fig. 47), is sometimes simple like a flat 

 drum and at otlier times undulated, as above stated of the 

 fossil diatom. This undulation is not uncommon in the frus- 

 tules of the DiatomacoH;, ex. gr. Actinocyclus tmdulatus and 

 Cymato2)hura, Besides the presence of this diatom in great 

 numbers, there are fragments of beaded strings very like those 

 of Melosira, often, when the moniliform divisions have become 

 separated, simulating the siliceous balls of a Geodia^ which 

 they exceed greatly in number. 



I have not seen any spicules of the genus of fossil sponges 

 to which I have given the name of " Monilites^^'' so common ia 

 the Upper Greensand of Ilaldon Hill (' Annals,' 1871, vol. vii. 

 pi. ix. figs. 44-47), and common also under the " acuate and 

 short-shafted three-armed headed forms," respectively, in the 

 cavities of the chalk-flints in the south of England (' Annals,' 

 1874, vol. xiv. p. 253), also present in the remains of the 

 chalk in the north of Ireland (Wright, ' Belfast Nat.-Hist. 

 Club Report,' 1875, pi. ii. figs. 4 and 5), unless M. Rutot's 

 fig. 21 be one. Nor have I ever seen any recent sponge 

 bearing spicules of this kind. 



Having thus described the " tubulations sableuses," we 

 arrive at the consideration of what they originally were ; and 

 here we must, to a great extent, depend on inference and con- 

 jecture. 



In the first place the vertical position of these fossils (some- 

 times, according to M. Vanden Broeck, "1 m^tre" in length), 

 with their small end or tail downwards, in an arenaceoiis 

 deposit, together with the tubular form, is more characteristic 

 of an Annelid than of any other animal ; while the forms of 

 the internal structures respectively are still more characteris- 

 tic of this kind of animal. To assume that any invertebrate, 

 such as a sponge, continued living during the time that a 

 "nig^re" of this arenaceous material was being deposited, 

 seems impossible, while an Annelid, or AspergvUum, indeed, 

 might bore down this distance in a very short period. 



Again, the central cylinder and its markings are almost 

 identical in form, size, and composition with those of Trachyr 

 derma serrata^ Salter (Quart. Journ. Geol. Soc. Lond. vol. xx. 

 parts, no. 79, Aug. 1, 1864, p. 288, pi. xv. fig. 9, a, 5), 

 common in the Silurian quartzite pebbles of this beach (Bud- 

 leigh-Salterton, Devon). But then the tubes or cylinders 

 here are aggregated, while the " tubulations sableuses " ap- 

 pear to be solitary. 



In the oval or compressed cylinder, too, we have the lobular 

 form indicative of original segmentation, and the linear depres- 



Ann. & Mag. X. Hist. Ser. 4. Vol. xix. 27 



