206 HH. A. Nicholson on Cornulites and Tentaculites, ete, 
there have not been wanting observers who would place Cornu: 
lites amongst the Pteropoda. 
The shell of Tentaculites, as in well known, has the form of a 
o specimen of Tentaculites has ever been found attached to 
any foreign body ; and though this of itself would not be fatal to 
the view that the genus belongs to the Zubicola, the mode of 
occurrence of the fossil completely negatives this supposition. 
Thus, Tentaculites are usually found in great numbers together, 
often over large areas, confusedly scattered over the surfaces of 
the laminae of deposition. If we had to deal with a tubicolar 
annelide, it seems certain that specimens would be found im 
bedded vertically in the rock, with the closed apex downwards, 
and the aperture directed upwards; or élse we should find 
them attached by their smaller extremities to shells and other 
foreign objects. On the contrary, the aspect presented by 4 
slab covered with Zéntaculites is precisely that which would be the 
result of the fortuitous aggregation on the sea-bottom of a num- 
ber of small shells, sinking from the upper strata of the ocean. 
All the evidence, then, at present in our possession goes to 
show that Tentaculites was an oceanic genus, comprising minute 
pelagic creatures which swarmed at the sarface of the Silurian 
seas, and the shells of which were scattered in myriads on the 
other, having all the characters of Cornulites.” It might, there 
fore, in some cases, be impossible to decide whether a give? 
