541* 



CORRIGENDA. 



I have to request the reader's attention to the following corrections, which I wish to 

 make in regard to some points in the preceding paper. 



1. The form represented in fig. 52, Plate XI., as a modification of Campylodiscus Ralfsii, 

 Sm., is, as I am now convinced, entirely distinct from that species, which in fact, occurs in 

 some of the dredgings along with it ; and, in addition to its being uniformly small, exhibits a 

 very different aspect. Fig. 52 agrees with the description given by De Brebisson of his 

 C. decorus, and I have no doubt belongs to that species, which must therefore be added to 

 the list of British Diatoms. 



2. Additional observations have satisfied me, that the form represented in fig. 95 e, 

 Plate XIV., is not a form of Amphora granulata, but an entirely distinct species, to be more 

 fully described at a future time. 



3. I wish to mention, that although I cannot see any reason to separate the two forms, 

 represented in figs. 80 b, and 80 c, Plate XIII., from Amphora spectabilis, fig. 80, so far as the 

 simple view of the latter is concerned, I have not yet been able to trace the complex structure 

 of A. spectabilis, shown in fig. 80<i, in these smaller forms. Whether this is because I have 

 not yet employed the highest powers of the microscope for this purpose, since these small 

 forms have much finer markings than the larger one, or whether the complex structure 

 occurs in the larger alone, while the smaller remain always simple ; or whether, finally, the 

 two smaller forms belong to a different species, are questions which I cannot yet answer. 



4. Having, by the kindness of Dr A. S. Donkin, of Morpeth, been enabled to examine a 

 most interesting marine gathering made by him, in which several of the forms described in 

 this paper, as well as several of those yet to be described as occurring in the Clyde, are met 

 with, I have now to state, that I find Amphora Grevilliana in that gathering, with almost 

 exactly the form and aspect of Amphora complexa, fig. 90, Plate XIII., while detached seg- 

 ments also occur, evidently belonging to it, and having the straight dorsal margin, but yet in 

 all other points agreeing with those of A. Grevilliana, as shown in fig. 36*, of my third plate 

 of Glenshira forms, and as seen in the present paper in the entire A. Grevilliana, fig. 89, Plate 

 XIII. I have therefore to withdraw A. complexa as a distinct species, and to request the 

 reader to consider the figure (fig. 90), as representing one view of a straight-sided form of 

 A. Grevilliana. In this variety, as seen in Dr Donkin's gathering, and as I have also 

 observed in the Glenshira Sand and in the Clyde, the detached segments are much narrower 

 than when the dorsum is convex. I have specimens of the convex segments, from the Clyde, 

 nearly three times as broad as Dr Donkin's, with the straight dorsum. I would further 

 observe, that in all probability, fig. 89 represents a frustule, or possibly a half-frustule, 

 viewed from the flat or concave side, while the frustule in fig. 90 is seen from the convex 

 side, so that the flat-lying lateral segments are not so distinctly seen. I must remind the 



VOL. XXI. PART IV. 7 F* 



