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PROCEEDINGS OF SOCIETIES. 
alone, whether we have a Polyzoan or a Sertularian under examination, 
and we are only able to solve the question by reference to the soft parts 
of the animals. The only author who has, as far as I can learn, written 
on the subject,'whose opinion is worth any attention, is the late Professor 
E. Eorbes, and if I venture to differ from his published opinions, it is 
because my conclusions are based on a careful study of the rocks and 
fossils, on a more extended scale than had been made by him. At the 
same time I freely admit that it is extremely difficult to adduce any ar¬ 
guments in favour of the Hydrozoan nature of these fossils which will 
appear conclusive on paper, this conclusion being the result of a careful 
consideration and comparison of such details of structure as the fossils 
afford, and based on characters of a general nature, drawn from appear¬ 
ances, even tangible enough to the eye, but utterly impossible to be 
described with precision. I cannot discover or appreciate what the cha¬ 
racters are which lead Professor Eorbes, ‘ ‘ speaking of their possible 
Polyzoan nature,” to use the words, an alliance more in accordance with 
the minute structure; careful casts, taken from Old. antiqua and from 
specimens of Sertularia argentea imbedded in plaster, are so much alike, 
that some years since they would certainly have been pronounced not 
merely generically, but even specifically, identical. 
Fig. 2. 
Two distinct forms at least of these fossils exist, both of which were 
named by Professor E. Eorbes, and have been described somewhat at 
length by me in a paper read before the Geological Society of this city 
(vide “ Proc.,” vol. viii.). They differ so much that I almost question 
the convenience of associating them under the same genus, one (Eig. 1) 
being furnished with a distinct axis, from either side of which alter¬ 
nately ranged branches proceed at regular intervals ( 0. antiqua ), whilst 
the other (Eig. 2) is destitute of any axis, made up of many stems of 
irregular length, springing from a common point, so that the fossils 
flattened from above present the form of a star, more or less regular ac- 
