38 POST-TERTIARY LACUSTRINE SAND 



We have thus in the Glenshira sand 210 known and de- 

 scribed species, with the exception of one or two recently 

 observed and likely to be soon figured. But I feel quite 

 assured that there are a good many more, belonging to this 

 category, which I am unable clearly to identify, from the 

 want of good figures, especially in those genera to be figured 

 in vol. ii. of Mr. Smith's Synopsis. In particular, there 

 appear to be several discoid forms of the genera Melosira and 

 Orthosira, &c., which will be found to be of known species. 



Let us now turn to those forms which appear to be un- 

 described, of which the proportion is unusually great in this 

 deposit. It has been already mentioned that only about one- 

 half of these forms can be figured on the accompanying plate, 

 and that the remainder will be given in the next number of 

 the ' Journal.' It will probably be best to describe the forms 

 here figured as they occur on the plate, in which the order of 

 the Synopsis is followed. It must be borne in mind that some 

 of the figures represent varieties of known forms, and that the 

 two first belong to the two new forms observed by me in the 

 Lillhaggsjon and Liineberg deposits, and described in last 

 number of the ' Journal.' 



Fig. 1, Plate IV., shows two forms of Eunotia Falx, W. 

 G. This very remarkable form needs no farther descrip- 

 tion beyond what will be found in the ' Transactions of the 

 Microscopical Society,' vol. ii,, p. 105. It has not yet oc- 

 curred as a British form. It occurs with fresh-water species. 



Fig. 2 lepresents an example of Nitzsckia Sigmatella, 

 W. G., also observed in the two deposits just named. But 

 it occars, as I have formerly stated, in the Mull deposit also; 

 and since describing it I have found it, not only in the sand 

 of Glenshira, but also in a recent gathering from Elchies, in 

 Banffshire. It is therefore a British species, and, from the 

 Banffshire locality, belongs to fresh water. (211.) 



Fig. 3. Cymbella truncata, W. G. This pretty and well- 

 marked species occurs in the Mull deposit, but sparingly. It 

 is frequent in the Glenshira sand, and cannot, I think, be 

 referred to any of the species of Cymhella or Cocconema, 

 figured by Mr. Smith. Of course it is impossible, in a fossil 

 deposit, to ascertain whether it be really a Cymhella, that is, 

 free, or a Cocconema, that is attached by a stipes. It is pos- 

 sible and even probable, that this species has been noted on 

 tlie Continent, but I have not been able to see any figure with 

 which it can be safely identified. It is very uniform in its 

 characters, always exhibiting the truncate or square ends from 

 wliich I have named it. It is sometimes a good deal longer 

 than the figure here given, which may be taken as typical. 



