StoddeRj on Diatomacece. 
27 
recall Dr. Gregory^s query^ whether they should not all be 
considered one species. The same observations apply to 
Navicul(B of the type of N. lyra. 
There are two forms of Ehrenberg^s genus Actinocyclus, 
called by most QA\.i}ioY\i\Q^Eupo discus ; one resembles jS.^^ar^w*, 
Greg. E. tenellus, Breb.^ and the Actinocyclus of Ehrenberg 
CMic. Geol.^ Taf. xix^ fig. 5^ c. 10). Also Coscinodiscus lunce 
(Tab. 35a;, group xxi, fig. 7) ; Cos. gemmifer (Tab. 3 5 group 
xxii, fig. 3) . This form is distinguished by rays composed of 
lines of contiguous dots, with other dots irregularly scattered 
between the rays. The number of rays is very variable, from 
six upwards ; sometimes the rays are so crowded, that the inter- 
mediate dots almost form continuous rays, only distinguish- 
able by their irregular distance from each other; colour, 
usually some shade of brown. 
The other form of Actinocyclus has very fine lines for 
rays, not always continuous ; and the whole surface of the 
disc is covered with a very fine network of, probably, hexagonal 
markings, too fine to be well made out with my instrument. 
This form is represented by Eupodiscus fulvus, W. Sm., and 
possibly by E. subtiliSj Ralfs ; by a great many of Ehrenberg^s 
species, ^Mic. Geol.,^ Tab. xviii, fig. 8, c. 18, Richmond, 
„ ,, xxviii, gr. 22, fig. 7, 
„ xxxv,A, gr. 17, fig. 1, and 2, guano, 
„ „ „ gr. 18, fig. 1,2, and 3, guano, 
Saldanha Bay ; 
also Strafford Cliffs and Bappahanock Clifls, var. colour, 
usually blue or purple, sometimes brown, and sometimes 
colourless. Both of these forms have generally, but not 
always, a nodule or process near the margin, resembling the 
" feet " of Eupodiscus and Aulacodiscus ; which is probably 
the reason of their having been taken for Eupodisci, though 
the structure of the valve appears entirely difierent from the 
true species of that genus. Ehrenberg does not figure or 
describe the nodule, but on examining the Actinocycli of 
Saldanha Bay, in the Bailey collection, received, I believe, by 
Bailey from Ehrenberg, I find the nodule is present in them. 
Ehrenberg^ s figures are sufiicient to indicate the genus, 
but not the species, except by the number of the rays, which 
is not a good specific character, neither is colour. But I am 
well satisfied that many of the so-called Eupodisci are 
Ehrenberg^s Actinocyclus ; in fact, it is almost admitted by 
Smith. 
These two forms of Actinocyclus should probably be placed 
in two genera. They have quite a different structure ; that 
of the first-mentioned is not cellular, but the dots are pro- 
