540 



PROFESSOR GREGORY ON 



Fig. 97 & 97 b, 



— 98 & 98b, 



Amphora cymbifera, n. sp., simple 

 and complex views, 97 c; 

 detached segment of do. 

 proboscidea, n. sp., simple 

 and complex views, 98 c, 

 and 98 d ; detached seg- 

 mentsof do. 

 99. Amphora costata, Sm., detached segment. 



— 100 & "1 bacillaris, n. sp., simple and com- 



100 b, j ' plex views. 



— 101. Navicula (?) Libellus, n. sp., 101 6 ; do, edge 



view. 



— 102. Nitzschia (?) panduriformis, n. sp. 



— 103. ... distans, n, sp., 103 b, do. S.V. 



— 104. . . . hyalina, n. sp., 104 b, do. S.V. 



ig. 105)™ 



klO'fc ( , " leurosi g ma • reversum, n. sp. 



& 



— 106. Sceptroneis Caduceus, Ehr. 



— 107. Synedra undulata, Greg. (Toxarium undula- 



tum, Bailey). Two specimens of the 

 S.V., the one straight, the other arc- 

 uate. 



— 108. ... Hennedyana, n. sp., S.V. 



APPENDIX. 



109. Creswellia (nov. gen.) Tunis, n. sp., Arnott. 

 All the above are magnified 400 diameters. 



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. I wish to observe, that after a very careful com- 

 parison of this form with N. Hennedyi, I 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 striae, 

 in the fineness of the striation, and in its very peculiar colour and nebulous 

 aspect. In all these points, N 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 N. 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 Bombtis, Ehr., fig. 12. This form also has occurred abundantly in 

 certain densities, and I am 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- 



