Diatomaceous Sand of Glenshira. 
85 
the striation nearly covers the whole frustule on the F. V., 
which we never find in Navicula or Pinnularia. Moreover, 
although the form is frequent, the S.V. which, as in ^4. vitrea, 
would much resemble a Navicula, does not occur, or at least 
I have not been able to find it, although I can trace both the 
F. V. and the S. V. in all the species oi Navicula and Pinnu- 
laria which I have been able to distinguish. For these 
reasons I suspect it to be of a different genus, probably an 
Amphiprora; but as this is doubtful, I figure it as a form to 
be further examined. (304.) 
53. Disc. This form, represented in fig. 52, is in all pro- 
bability not Diatomaceous, but one of the Polycystinece. It is 
a very beautiful object, and is made up of large hexagonal 
cells, the disc having a raised border or margin of considerable 
breadth, crossed by what appear like rings projecting on the 
circumference. Diameter about 0 002". Many of the cells, 
which otherwise resemble those of Eupodiscus Argus, or of 
Triceratium Favus, have a punctum in their centre. 
Not being familiar with the Poly cystines, I figure this disc 
in the hope that some one who is familiar with them will be 
able to say whether it be one or not. It is at all events a 
fine object, and is very scarce indeed in the deposit. I 
observe a few very similar discs in an earth sent to me by 
Professor Bailey, marked, Bermuda tripoli, locality doubt- 
ful. (305.) 
54. Oval form, fig. 53. When I observed this curious 
form with a low power, it seemed to resemble an Amphora ; 
but on closer examination this resemblance disappeared, and 
I found myself unable to refer it to any genus known to me. 
Indeed, I have considerable doubts whether it be Diato- 
maceous, and suspect that it may prove, like the preceding, to 
belong to the family of the Polycystinece. The specimen is 
unique, up to this time, in the deposit. 
General form oval. The upper end seems to show an acute 
interior point, from which the external covering has been 
broken away, so as to expose it. At the lower end it appears 
to terminate in a cylindrical neck, which is truncated near 
to the body. The surface is marked by concentric lines of 
large and somewhat distant dots, these lines being arranged 
in pairs, the two of each pair rather close, but the interval 
between two pairs much wider. Of these pairs of lines, four 
are visible. Length about O'OOl". On the whole, it seems 
to be more like one of the Poly cystines than a Diatom. 
(306.) 
Such is a brief account of the forms I have found in the 
Glenshira Sand, in addition to those formerly described, and 
