Diatomaceous Sand of Glenshira. 
75 
vex. I have not been able to see this surface as if looking 
directly down on it^ although the form is not rare in the coarser 
densities ; but I have no doubt that the frustules may be 
picked out and examined in water or some other fluid in which 
they can be turned round so as to show all the faces. 
The above description applies, mutatis mutandis, to A.crassa, 
and, as I believe, also to A. Arcus; and although these forms 
aU exhibit some points of agreement with AmphorcB, as 
hitherto known, yet the peculiarly complex structure of each 
half of the frustule seems to be a character so marked, as to 
require a new genus for those forms in which it is found, I 
do not, however, venture to establish such a genus, but am 
satisfied to direct the attention of observers to the existence 
of this remarkable structure, (which appears also to occur in 
A. cost at a, figured in the ^ Synopsis,^ vol. i,) in the hope that it 
may be more thoroughly investigated and more satisfactorily 
cleared up than I have been able to do it. I should here add, 
that possibly A. biseriata, the structure of which is both 
obscure and peculiar, may iDclong to this group, and that even 
A. plicata may be found to be related to it. (289.) 
(A. Grevilliana, as well as the next species, occurs in the 
recent gathering already alluded to.) 
37. Amphora Arcus, n. sp. Of this species, individual 
segments were figured in my former Paper. I had not then 
seen it entire ; but since then I have found that one of the 
complex, barrel-shaped forms in the deposit belongs to it, and 
is either the entire frustule or half of it. Like A. Grevilliana, 
it varies considerably in length, but the entire or half frus- 
tules I have seen have been shorter than many of the de- 
tached segments. The general structure and form resemble 
those of the preceding species ; but the segments are simply 
arcuate, having the form of a strung bow. The entire frus- 
tule has the form of a barrel with ribs and bars, and all parts 
are easily distinguished from A. Grevilliana by their coarser 
striation, and by the coarsely moniliform character of the 
striation. As the segments were formerly well figured, I give 
here a figure of what is not the entire form, but is more 
probably only one half of the barrel. This is represented in 
fig. 37. (213.)^ 
38. Amphiprora minor, n. sp. This species, represented in 
fig. 38, is not very rare in the deposit. 
Form elliptical, long, and rather narrow, the central part 
slightly constricted. The inner margin of the lateral parts is 
concave towards the middle, leaving a long, narrow, truncate. 
* So 11 u inhered in Part I. 
