MICROPLANKTON 217 



is correct in accepting Pavillard's specific name on grounds of priority (Pavillard, 191 1, p. 24, 

 fig. ib, c; Mangin, 1912, p. 39, fig. 25, pi. II, fig. 10). 



The intercalary bands arranged in imbricating fashion were hard to see in some of the colonies, and 

 many of the frustules resemble the two lower ones in Pavillard's figure, where the bands are visible 

 only where they approach the cell margin as seen in broad girdle view. Such banding on the con- 

 nective zone is a rare feature among Chaetocerids, viewed under ordinary conditions, but characteristic 

 of the related genus Attheya. 1 



Some of our material even suggested that Chaetoceros imbricatus Mangin (191 2, fig. 37) should also 

 perhaps be considered as a synonym of C. costatum Pavillard, the cells in the chains were so closely 

 adpressed, but I could not feel sure of distinguishing between these forms and phases of C. didymum 

 like the var. agregata also figured by Mangin (191 2, fig. 37) from the type locality of his C. imbricatus 

 off Brest, under the working conditions imposed by normal plankton analysis. C. didymum was 

 exceedingly abundant, in a welter of varieties or phases, at most inshore stations during our Benguela 

 current survey. The question must be left open, with the admission that further detailed work may 

 serve to show the presence of C. imbricatus Mangin here, and that it may have been wrongly included 

 with C. costatum Pavillard, or with some phase of C. didymum in my counts. As the numbers involved 

 were exceedingly small in comparison with those of clearly indentifiable species, the point is of small 

 .moment in considering the diatom flora as a whole. 



Chaetoceros subsecundum (Grunow) Hustedt formerly known as Chaetoceros diadema (Ehrb.) Gran. 



Hustedt ( 1 927-37, p. 645) details the argument by which, under the International Rules for Botanical 

 Nomenclature, the widely known specific name diadema, finely descriptive of the resting spores, and 

 based on Syndendrium diadema Ehrenberg 1854, should be supplanted by the above combination, 

 based on C. distans (Cleve) var. subsecunda Grunow (ex Van Heurck, 1881 (1880-5). 



It appears that Grunow was right to reject diadema on realizing that the forms in question were 

 related to Chaetoceros, Syndendrium diadema becoming a nomen cofifusem, since it was based upon the 

 resting spores only. Unfortunately, Grunow was mistaken in relating it to C. distans Cleve (1873), 

 itself a misidentification of C. dichaeta Ehrenberg. It thus became necessary to elevate the varietal 

 name to specific rank as Hustedt has done, though there is still much doubt and confusion about the 

 full synonymy. 



I am greatly indebted to Mr N. I. Hendey for a personal communication helping to clear up this 

 obscurity. 



Rhizosolenia imbricata Brightwell var. (or phase) Shrubsolei Cleve, often previously considered 

 as a distinct species, R. shrubsolei Cleve. 



Our Benguela material of this usually small and narrow form of comparatively cold waters seems 

 to me to provide ample support for the view that it is not specifically distinguishable from the stouter 

 form of warmer seas described as R. imbricata by Brightwell. 



Hustedt (1927-37, p. 584) gives formal expression to this view, and points to the synonymy with 

 R. striata Greville and the apparent lack of justification for the establishment of Peragallo's R. atlantica 

 and R. pacifica, both seemingly also synonyms of R. imbricata Brightwell. 



A footnote of Gran's (1905, p. 52) anticipates Hustedt's decision, pointing out that if the specific 

 identity of the two forms could be demonstrated, Brightwell's name should be the one used on 

 priority grounds, and it would seem that Cleve himself had drawn attention to the matter. 



At several Benguela current stations both forms were present, mainly very much as figured by 

 Lebour (1930, p. 97) under the name R. shrubsolei Cleve, but many individuals intermediate both with 



1 Intercalary bands have also been described in Chaetoceros teres, visible only after special treatment and mounting (Mangin, 

 1908) and in Chaetoceros eibenii by Pavillard (1921). 



%$■ , 

 ^OODs 



