ON SOME DIATOMACEJE FROM THE ISLAND OF SOCOTRA. 513 
On some Diatomace: from the Island of Socotra. By F. Kr os, 
Hon. F.R.M.S. (Communicated by Lieut.-Col. H. H. Gop- 
WIN-AUSTEN, F.R.S., F.L.S.) 
[Read March 20, 1884.] 
(Prats XLVIII.) 
Tn material in which the following Diatomacee were found was 
obtained by Prof. Bayley Balfour during a short visit to the island 
in the cold season of 1880, and consisted of a mass of water-plants 
containing small freshwater shells (the plants were I believe 
gathered and brought to England as botanical specimens, and the 
shells were living on them). Colonel H. H. Godwin-Austen, to 
whom they were sent, after picking out the shells, washed the 
plants, and placed a drop of the washing under the microscope and 
detected some diatoms in it; the remainder he sent to Dr. Bossey 
of Redhill, from whom I received it with a request that I would 
make * a list of the species contained in it; to report whether 
it contained any one species peculiar to the island, and whether 
the whole collection or any one species may indicate connexion 
with Africa or India by land- or water-carriage, or by former 
continuity of land." 
After cleaning the crude material and eliminating the vege- 
table débris and coarse sand, sufficient diatoms and fine sand 
remained to fill about jj; of a small homeupathic tube. This 
I divided into two densities: the heavier, eontaining the larger 
forms and sand, was minute in quantity, yielded a new species 
of Cerataulus, but by no means in abundance. I have probably 
seen about thirty specimens; but, from its delicate nature, most 
of them were broken. 
The genus Cerataulus was constituted by Ehrenberg in 1843 to 
receive a single species, C. turgidus.  Grunow, in 1863, amended 
the genus and added Biddulphia levis, Ehr., and two new spe- 
cies of his own. All species of the genera Cerataulus and Bid- 
dulphia are marine. Although I do not think that there is suffi- 
cient generic distinction to warrant the constitution of the genus 
Cerataulus, I have retained it for the Socotran diatom from 
its great resemblance to C. levis. Indeed the resemblance is so 
close, that a casual observer would at once refer it to that species. 
A. careful examination and the employment of a high power 
show some important distinctions: the striw of the latter are 
LINN. JOURN.— BOTANY, VOL. XX. 2T 
