540 PROFESSOR GREGORY ON 
Amphora cymbifera, n. sp., simple | Fig. 105 t 
Fig. 97 & 97 b, { - eee complex ae Ove: 2105 > |Pleurosigma ¥ reversum, 0. sp. 
detached segment of do, | — 106. Sceptroneis Caduceus, Ehr. 
proboscidea, n. sp., simple | — 107. Synedra undulata, Greg. (Toxarium undula- 
— 98&98b and complex views, 98 c, tum, Bailey). Two specimens of the 
? and 98 d; detached seg- S.V., the one straight, the other arc- 
mentsof do. uate. 
— 99. Amphora costata, Sm., detached segment. — 108. ... Hennedyana, n. sp., S.V. 
—100& | bacillaris, n. sp., simple and com- 
100 b,j ** plex views. 
— 101. Nayicula (?) Libellus, n. sp., 1016; do, edge APPENDIX. 
view. 
— 102. Nitzschia (?) panduriformis, n. sp. — 109. Creswellia (noy. gen.) Turris, n. sp., Arnott. 
— 103. Pe distans, n. sp., 103 b, do. S.V. All the above are magnified 400 diameters. 
— 104. 2: hyalina, n. sp., 104 b, do. S.V. 
Postscript. 
While the preceding pages were passing through the press, I have been able 
to examine with care numerous specimens of most of the forms there described, 
and I wish here to modify to a small extent some of the views I have expressed. 
In every instance, I speak after the comparison of a very large number of fine 
examples. 
1. Navicula nebulosa, fig. 8. 1 wish to observe, that after a very careful com- 
parison of this form with V. Hennedyi, | have no longer any doubts as to its 
being a distinct species. I find it remarkably uniform in its characters, and par- 
ticularly in its oval form, with the ends on the whole broadly rounded, while it 
has a slight angularity in the middle, and a slight trace of acumination at the 
apices. It is equally uniform in the narrowness of the marginal band of strie, 
in the fineness of the striation, and in its very peculiar colour and nebulous 
aspect. In all these points, V. Hennedyi differs from it, as I have stated. But 
while these points of difference appear trifling, and are difficult to express in 
words, I must observe, that there is no real resemblance between the forms, and 
that when, as often happens, both being frequent, they occur close together, and 
of equal size (though V. Hennedyi is usually a larger form), it is quite impossible, 
even under a low power, to confound them together, the whole aspect of the two 
forms being remarkably different. 
2. Navicula spectabilis, fig.10. Having found, in certain densities, many very 
fine specimens of this form, I have to state, that it occurs of nearly twice the 
size of the individual figured, and that it is perfectly uniform in its characters. 
3. Navicula Bombus, Ehr., fig. 12. This form also has occurred abundantly in 
certain densities, and Iam now quite satisfied that it is a distinct and well-marked 
species. In the description I have omitted to mention an important character, 
namely, that it is never, literally,—not in one out of thousands of examples—sym- 
