150 
West, on Diatomacea. 
All the species of Asterionella at present known are 
extremely hyaline, almost disappearing in balsam; on 
A. formosa, dry, I have, with high powers, seen faint indica- 
tions of striae. The present species will probably prove to be 
far from uncommon ; it has been found at Tenby, Harrogate, 
Norwich (for specimens from the two latter places I am 
indebted to Mr. F. Kitton), and in the neighbourhood of 
London. A curious fact connected with it is its discovery 
first in the waters supplied to these various places for drink- 
ing purposes. Dr. Hassall informs me that at certain seasons 
it is one of the commonest of the Diatomacese occurring to 
him in his examinations of London waters; and Dr. Lankester^s 
experience goes to confirm this. When growing freely under 
favorable circumstances, numerous frustules may adhere to- 
gether ; I have seen it from the Serpentine in this state — six- 
teen, twenty, and more, were not uncommonly united. I 
believe it is always free, or unattached. 
A. Ralfsii, W. Sm. (Fig. 9.) 
This species approaches nearest to Diatoma. I have seldom 
seen more than four or six in a star. It was gathered 
plentifully by Mr. Ralfs, for two years, in a little boggy pool at 
the base of Cader Idris, and 1 have seen it in a gathering of 
Diatomacese from Teignmouth. 
A. Bleakleyii, W. Sm. (Fig. 10.) 
Side view as in A. formosa ^ the attached extremity larger 
than in that species. 
By courtesy of Dr. J. E. Gray, I have had the opportunity of 
examining authentic specimens of this species in the collection 
at the British Museum. As many as sixteen or twenty frustules 
occasionally occur in union. Whilst on a visit to Colonel 
Baddeley, I had the pleasure of seeing, in a living state, 
numerous examples obtained from Noctiluca, which differed 
in the great inflation of the attached extremities, and the 
extreme slenderness of the frustule both on front and side 
view. I am unwilling, however, to consider this as more than 
a variety of the present species ; it was gathered by the 
late Mr. W. Brooks, at Walton-on-the-Naze. 
3. PoDosiRA, Ehr. 
P. 7 compressa, n. sp., T. W. (Fig. 11.) 
Frustules geminate, polar always much shorter than the 
equatorial diameter ; valves elliptic, indistinctly marked with 
scattered puncta; cingulum smooth. Breadth of long 
diameter of valve, -0008" to '0014''; of short diameter, -0004" 
to -0005". 
This interesting form has, I believe, only been met with as 
yet on the coast of Northumberland, where it was found by 
