Edwards_, on Diatomaceoi. 
89 
and radiatuSj botli of which have true elevated processes. 
Besides^ I have specimens of Coscinodiscus concinnus and 
subtilis bearing this pseudo-nodule ; and Mr. Roper^s Eupo- 
discus tesselatus also belongs to this group, as it has not the 
elevated process which distinguishes the genus Eupodiscus 
from Coscinodiscus. Indeed, there is a disc in the fossil 
stratum of Virginia similar to Mr. Roper's species, except 
that it is destitute of the pseudo-nodule. Mr. Roper him- 
self (^Transactions/ vol. vii, p. 19) has remarked this fact. 
The arrangement of the markings in Actinoptychus is similar 
to, though not precisely the same as in Coscinodiscus subtilis ; 
and this, in my opinion, warrants its being placed in Cos- 
cinodiscus, and it might be called C. actinoptychus. The 
number of radiations in this form, any more than in Actino- 
phcenia, cannot be considered as a specific distinction, as the 
number of radiations in any of the species of Coscinodiscus is 
not constant. There are one or two other discoid forms 
found in guano and a fossil state, that may belong to one or 
other of the genera mentioned above, but they have not been 
sufficiently studied to allow me to place them. 
There is also in this gathering a form which, at first, would 
seem to be a new species, but I am convinced it is only a 
variety of Podosphcenia Lyngbyei. On F.V. it has much the 
appearance of that species, and only differs in having the top 
portion squared ofi", similar to P. Ehrenbergii, but even more 
so than that species, so that it has an elbow on each side. 
The S.V. is entirely different from any of the known species, 
and is strongly inflated about two thirds of the way up, 
giving the valve somewhat of a lozenge form, only that the 
sides are concave. Both ends are acute. From the outline 
of its valve I should have been tempted to erect this into a 
new species, had I not remembered that outline can seldom 
be relied on as a specific distinction. Again, another, and 
conclusive, reason for considering this to be only a variety of 
P. Lyngbyei is, that in the same gathering are to be seen many 
intermediate forms uniting it with that species, which is very 
common at this locality. 
The Biddulphia lavis found in this gathering is the oval 
variety, which in my opinion is the normal form, the orbicular 
variety not being found at Hurl-gat, though common in the 
Hudson River at West Point. 
I have placed in my list of species Biddulphia reticulata ? 
of Roper, but am in doubts as to the propriety of assigning 
it to that species ; it may be a variety of B. aurita, but much 
resembles the finely marked form in his plate Trans. Mic. 
Soc.,' vol. vi, PI. IT, fig. 16). 
