35 
in 1844 (vide “ Proceedings of the Geological Society of Dublin,” vol. lil, 
p. 66)—among the list of fossils. But, although the former animal 
nature of these beings is now admitted, their exact position in the scale 
is by no means free from doubt; nor need we wonder at this when we 
recollect that but a few years since the two great families—to both of 
which Oldhamia has been referred by different observers, viz., the Poly- 
zoan Mollusca and the Hydrozoan Acrita—were confounded together, and 
that in many cases (widely different as the animals composing these two 
elasses are in the structure and relations of their organs), even among 
recent species it is impossible @ priord to declare, from the skeletons 
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. Forbes, 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 Forbes, ‘‘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. 
