334 Diatoms. 
Coscinodiscus, which is a round shell resembling a thick 
shilling, closely covered with dots on both sides, is worth 
mounting, when found ; but, being extremely brittle, great 
care must be used. The Gramataphora serpentina is found 
in great numbers, and is like a card case, with four curved 
lines running from opposite ends towards the centre. Dif- 
ferent kinds of avicu/e, or little ships, are to be found by 
careful examination; and they are very amusing when 
alive, for they run about and bump up against one another, 
then draw back after a time and swim away in the opposite 
direction. A few specimens of Pleurosigma hippocampus 
(Sea-horse), and some other varieties of these most beau- 
tiful objects, which are at once recognized by their form, 
which is that of Hogarth’s lines of beauty of different cur- 
vature joining at their ends, and having another which runs 
between them and expands in the centre, and at each end 
into round dots or spaces (which some say are openings; 
others, only a thickening of the central rib; but I am in- 
clined to believe the latter, from the manner in which the 
valve is broken on being pressed ; for the crack does not 
run across the dots, as it would do if they were openings, 
but round them, proving them to be stronger there than 
elsewhere). And all the rest of the surface is covered with 
rows of minute dots, arranged in regular rows, but so hne 
that, except with the very highest powers, nothing can be 
seen but longitudinal and transverse lines; and a 4-inch 
that will show even these may be considered very good. 
Pinnularia dactylus is like Surirella constricta, only much 
smaller and expanded instead of contracted in the centre. 
The Gallonela sulcata is a beautiful object, and resembles 
highly-carved ivory bones stuck end to end, so as some- 
times to form a filament appearing as much as three inches 
in length, when viewed under a good } inch power. Sym- 
phonema geminatum, which may be compared to a number 
of joined fans attached to a branched stalk by the end held 
in the hand; and Acnanthes longipes, which is a bundle of 
oblong boxes joined together and connected by a long ge- 
latinous stalk to the weed, complete the list of those from 
Southend which I have found; but I have no doubt that a 
much greater variety would be obtained if the weeds were 
collected at the proper time, 
A great number of the most beautiful forms are contained 
in fossil earth, which may be obtained from dealers in 
minerals. Those of Bermuda, Oran in Algeria, and Rich- 
mond, U.S., are the most important, and contain the 
