228 RECENT RESEARCHES IN THE DIATOMACE®. 
ons. It seems, therefore, that we have here a series corresponding 
to the post-glacial deposits which I have observed elsewhere, and 
exhibiting in the contained plants the gradual changes of climate 
from the forest-bed down to the boulder clay. 
RECENT RESEARCHES IN THE DIATOMACEZ. 
By Rey. E. O’Meara, A.M. 
Lae 
n the family Achnanthee the valves are symmetrical in the 
longitudinal axis, but unsymmetrical in the plane of separation; the 
frustules are more or less geniculate, so that of the valves one i 
possess a middle granular plasm-mass and t 
lying on the girdle-bands, and thence passing over the valves. The 
¢ , and separate by an 
cision proceeding from the ends. The well-defined cell-kernel lies 
ways ne 
ieces ; but 
termined. 
-he marine 4. longipes was observed by Smith in the act of 
forming auxospores, the same form, as well as A. subsessilis, by 
Liiders. In respect to the former Smith maintained that a single 
According to Liiders, there is always found a gelatinous sheath 
seeanrnd the infant cells, which force themselves out by an opening 
at the end. 
It appears confusing that two species so nearly related should 
exhibit such different conditions in the formation’ of their spores, 
a wish that observers residing 
i i a 
fter the Achnanthidee Pfitzer ranges the group Cocconeidea, in 
are embraced the two genera, Achnanthidium and Cocconeis. 
Achnanthidium has been distinguished from Achnanthes by the fact 
