SYSTEMATIC ACCOUNT 347 



valve structure of the Naviculaceae. Unfortunately the photosynthetic elements were 

 absent from all of the specimens observed, so no knowledge was obtained of the cell 

 contents. 



Observed at St. WS481. 



Genus Pleurosigma Wm Smith 

 Wm Smith, 1852 



The genus Pleurosigma was reviewed by Wm Smith in the first volume of his 

 Synopsis of British Diatomaceae (1853), p. 61, twenty-six species were described. In 

 vol. 11 of the same work (1856, p. 97) Smith explained that "the alliterative blunder in 

 the name Gyrosigma (Gyrosigma Hassall, 1845) must be my excuse for not adopting it as 

 the designation of this division of the Naviculaceae an excuse whose validity I find thus 

 admitted by M. de Brebisson in the brochure above quoted" [Brebisson, Diatomees de 

 Cherbourg (1854), p. 255]. 



As Pleurosigma was synonymous with Gyrosigma and the only excuse put forward by 

 Smith in support of his name was that he objected to the construction of the earlier one, 

 technically speaking, the name Pleurosigma was illegitimate and should be rejected in 

 favour of Gyrosigma Hassall. 



The genus Gyrosigma was established by Hassall in his History of the British Fresh- 

 zvater Algae (1845, p. 435) ; one species only was described. A footnote which appeared 

 upon the same page as the generic description informs us that Hassall's reason for 

 creating the genus Gyrosigma was that his aesthetic taste was upset also by the earlier 

 name used for that group of organisms namely Sigmatella. Hassall said " Sigmatella of 

 Kutzing, the construction of which term is somewhat objectionable, is synonymous 

 with Gyrosigma." Technically speaking, the same rule takes effect as in the case of 

 Pleurosigma, that is, Gyrosigma should be rejected upon the grounds that it is illegitimate. 



The matter becomes more complicated if pursued further. The genus Sigmatella of 

 Kutzing was validly published in 1833 (1833 a) ; one species only was described, namely 

 Sigmatella Nitzschii, which was based upon Bacillaria sigmoidea of Nitzsch. The same 

 species, Bacillaria sigmoidea Nitzsch, was taken by Hassall and used for the type of the 

 genus Nitzschia (Hassall, 1845, p. 435) under the name Nitzschia elongata. The position 

 is that two genera have been established upon one and the same type-species, and by 

 virtue of priority Kutzing's Sigmatella should be used to designate that group of 

 organisms now known as Nitzschia. If the name Nitzschia is preferred it must be 

 conserved. 



The position of the name Gyrosigma, however, is not quite so clear. It is possible that 

 a typographical error occurred on p. 435 of Hassall's book, and that the objection he 

 made to the construction of the name Sigmatella was really in support of his genus 

 Nitzschia which also appeared upon the same page, and was not meant to refer to 

 Gyrosigma, or, what is far more likely, Hassall intended Gyrosigma to designate a section 

 of Sigmatella of a later publication, that is, not Sigmatella Kutzing (1833 a) but Sig- 

 matella Kutzing in some other place. This suggestion gains support by the fact that 



