PROCEEDINGS OF THE SOCIETY. 
707 
It is rare, or concealed by the debris, in these slides, and I note two 
specimens, at Slide 1 ff, and Slide 2 §|. 
Surirella robusta E. Fragments observed. 
*Sijnedra longissima W. S. (V. H. S., xxxviii. 3). Very abundant. 
*S. Ulna E. 
I find at ff, f-f, Slide 2, and elsewhere, a diatom which is new 
to me, Y. lanceolate with subacute ends, and a central constriction in 
one side. Dimensions (of specimen ^): length, 0*05 mm.; breadth, 
0 • 01 mm. across lobes ; striae parallel, 13 in 0*01 mm., faintly punctate. 
The structure suggests Nitzschia , though if the keel is, as appears to me, 
on the convex side, it is in form unlike any species of that genus. 
Further examination under more favourable circumstances, especially of 
a frustule if it could be obtained, is necessary to determine this diatom. 
In the above list I have marked * the most numerous species. All 
are of freshwater habitat, excepting the four species specially noted as 
brackish or marine. 
The list presents no special facies, and, with the exception of a few 
forms which are not abundant, the species enumerated might be met 
with in any British gathering not far from the mouth of a river. 
The only species as yet recorded only from S. Africa, in addition 
to the Nitzschioid (?) form I have sketched, and possibly the doubtful 
Cymbella, is Stauroneis pachycephala Cl. 
Abbreviations used for References. 
S. N. D. — Synopsis of the Naviculoid Diatomacese. Cleve. (Stockholm, 1891.) 
D. E. N. — Diatomees Especes nouvelles. Brun. (Geneva. 1891.) 
Y. H. S. — Synopsis of the Diatomaceae of Belgium. (Yan Heurck.) 
N. & It. D. — On some new and little known Diatoms. Cleve. (Stockholm, 1881.) 
S. B. D. — Smith’s Synopsis of the British Diatomaceae. 
Mr. Comber said that Mr. Grove told him about these slides the last 
time he saw him, and although as a rule they contained just such species 
as might be expected to be found in any freshwater deposit here, there 
were two which seemed as if they were new, and of these the smaller 
one appeared to be a species of Nitzscliia. Mr. Grove was of opinion 
that it would be of much greater advantage if Mr. Cooper would send 
some of the material over for examination, instead of mounting the 
diatoms himself, because the slides in question showed some room for 
improvement in this respect, and the work of identification was not 
facilitated by specimens mounted in that way. 
Mr. Swift exhibited a microtome, which was made as an improve- 
ment upon the Cambridge Booking Microtome, at the suggestion of Mr. 
B. Smith, who had experienced some difficulty in cutting sections with 
the original form, especially of substances of unequal density. The 
chief feature was that it was here possible to fix the razor obliquely, and 
to vary its angle as might be found best suited to the substance it was 
desired to cut. It was also possible with this machine to cut sections 
of specimens imbedded in celloidin in spirit, and an arrangement was 
also provided by which they could cut sections of specimens frozen by 
ether. 
