MEMORANDA. 65 



the greater part large enough for the spring to work in 

 freely ; the smaller part at the top has brass wire fitted in, 

 which holds the spring. When a change of objective is 

 required, the knob e is drawn towards the stand, which with- 

 draws tlie bolt; /, the cover to keep dust out of the object 

 glasses not in use. 



In amount of projection, the centre of each "nose" is 1-3- 

 inch from centre c. 



I believe a quadruple nose piece might be made to work 

 well on the same plan; but it is rare that four objectives 

 are needed at one time, and the loeight of the whole would, 

 probably, be inconvenient. — John Burton. 



Fossil Diatomaceae. — In the January number of the ' Quar- 

 terly Journal,^ in a paper communicated by F. C. S. Roper, 

 Esq., F.L.S., F.G.S., &c., on some undescribed species of 

 diatoms, by George Norman, Esq., of Hull, there is one 

 figured on PI. II, fig. 3, called the Coscinodiscus fuscus, and 

 described in the text, the habitat is described as the stomach 

 of marine Ascidians, North Sea. 



On examining my slides of Diatomaceae a short time since, 

 I was struck by finding one similar in appearance ; the slide is 

 labelled " Fossil Diatoms from Guano." Having the ' Journal ' 

 by my side, I compared notes, and measured my own, and 

 thus describe it : valve convex, depressed in centre so much 

 so that on using an -^th it is impossible to get the centres 

 and edges accurately in focus; at the same time striae 

 ranged in parallel lines, diminishing in number. At intervals 

 dots about 20 in •001" ; valves variable in size from 002" to 

 006" ; in colour they are light blue, and in a few darker at 

 the edges. They are by no means rare, as the slide is com- 

 posed of about 15 or 20 per cent., the remaining portion 

 being the C. radiatus figured in the ' Micrographic Diction- 

 ary,-' PL xviii, fig. 32, these are very coarsely marked. I 

 must now difi:er a little, if I am allowed to hold a contrary 

 opinion to so eminent an observer as Mr. Norman, but 

 what he calls granules I call areolce or depressions. I have 

 tried the C. fusciis with every variety of light,, and as seen 

 in some portions they look very much like granules lying 

 upon the surface of the valve ; on applying a very high power 

 and humouring the light so as to get it at the proper angle, 

 they are distinctly seen (at least I think so) to be pits quite 

 through the valve. I have been farther led to this con- 

 clusion by a careful examination of the C radiatus, a kin- 

 dred genus of the same habitat. These with a power of 750 

 diameters, and oblique light, show distinctly to be foramina, 



VOL. II. NEW SER. E 



