70 
Dr. Gregory, on the Post-tertiary 
tellum, but I have considerable doubts on this point. The 
form figured by Roper as C. concentrica is referred in like 
manner to C. Placentula, but this also is doubtful. In the 
Glenshira Sand both of these are frequent; and there is 
another form, allied to C. concentrica, but differing still more 
from C. Placentula. This form is a curious one, but I have 
not yet been able to study it properly. 
29. Amphora {?) rectangularis, n. sp. This is a pretty little 
form, which I refer to Amphora on account of the crossbar in 
the middle of each valve ; otherwise I should have referred it 
to Amphiprora. Represented in fig. 29. 
Form of the entire frustule nearly rectangular, narrow, with 
the corners somewhat rounded. The middle space is widest 
at the ends, and in the centre ; narrower between these points. 
The striated portions are crossed by a straight bar, opposite to 
which the outline is slightly constricted. Length from 
0-0025" to 0-0045". Stri« fine, transverse, about 40 in 0-001". 
Besides the central constriction, the external margin is very 
slightly undulated towards the ends. (283.) 
30. Amphora elegans, n. sp. This form is frequent, as is 
also the preceding ; but it seldom occurs entire, and the figure, 
fig. 30, is that of the detached valve. 
Form of the entire valve oval, elongated, with truncate ex- 
tremities. Length from O'OOl" to 0 0025". The two halves 
are separated by a rectangular space. The curve line in each 
valve is peculiarly gentle and beautiful. Each valve is crossed 
by a line or bar in the middle. Aspect hyaline ; striae very 
fine, transverse, inconspicuous. 
(1 have lately found it entire in the recent gathering above 
mentioned.) 
31. Amphora plicata, n. sp. This is another hyaline 
species. Fig. 31 shows the entire frustule, which is frequent; 
but its parts are often shifted or displaced. 
Form nearly rectangular; broad, corners rounded, ends 
truncate, the middle part of the outline being slightly convex 
or elliptical. In some it is quite straight. The curve line in 
each valve very deeply curved, the curve coalescing with the 
margin near the ends, and projecting much towards the 
nodules in the middle. The part of the valve external to this 
line is very faintly marked with transverse striae, difficult to 
be seen, from the hyaline character of the form. The median 
space is marked by strong vertical, or rather concentric, 
slightly curved lines, which appear as folds, like those of 
paper plaited and then partly opened out. I have named it 
from this character. It is a beautiful and striking form, but 
apt to be overlooked from its transparency. (284.) 
