the pith-cylinder was a calamite-like structure, but in 
which the woody cylinder was “ composed in part of scalari- 
form or reticulated vessels, and in part of wood cells with 
one row of large pores on each side/’ the whole being sur- 
rounded by a bark ribbed longitudinally like a sigillaria. 
Some English phytologists have doubted the accuracy of 
these observations made by Dr. Dawson; but the specimens 
described by Prof. Williamson strangely confirmed their 
probable accuracy in all points, demonstrating the existence 
of a coniferous type of Calamites containing true medullary 
rays of the mural form. 
Erratum. — Page 31, line 11 from the bottom, for result 
read amount. 
