142 Scientific Proceedings, Royal Dublin Society. 
formed by the union of rings developed around the protruded 
ends of the polypides, rather than by any regular disposition 
of rod-like scale. But we have, thanks to the researches of 
Nicholson, Hall, and Ulrich, a beautiful series of Fenestellids 
from Carinopora, Nich. (11, p. 81), Unitrypa, Hall, and Isotrypa, 
Hall, to the well-established Hemitrypa, Phill. We may con- 
ceive how the keels of Carinopora were useful for the protection of 
greatly extended polypides; how scale, slight and irregular, or 
finally more massive, as in Unitrypa and Isolrypa, would serve to 
support the anterior portion of these animals; and how, indeed, a 
permanent protrusion of the polypides may have occurred, the 
tentacles then arising at the well-arranged tegminal apertures, 
while a membraneous tube, perhaps, extended back from each of 
these to the true zocecial opening. ‘This is, however, clearly 
a difficult matter for speculation. The elementary conception of 
the Fenestellid zocectum as a simple cyclostomatous calcareous 
tube has, at any rate, been long ago dispelled by the preparation 
of microscopic sections. 
In addition to those friends whose kindness has been acknow- 
ledged in the paper, I would express my indebtedness to Professor 
H. A. Nicholson, ¥.n.s., Mr. G. H. Carpenter, B. sc., and especially 
to Dr. G. J. Hinde, Vice-President of the Geological Society of 
London. 
! Cryptopora, Nich. (11, p. 77), from Ontario, cannot be regarded as completely 
known. It seems possibly a true Hemitrypa. 
