2 66 DISCOVERY REPORTS 



Genus Arachnoidiscus Bailey ex Ehrenberg 

 Nomen conservandum 



Inter. Rules Bot. Nom. (1935), p- 119. 



Ehrenberg, 1849. 

 Hemiptychus Ehrenberg, 1848. 

 Arachnoidiscus Bailey ex Ehrenberg, 1849. 



There appears to have been a confusion in the literature concerning the authority for 

 the generic name. Brown (1933) proceeded at great length to elucidate the history of the 

 name, and yet, after clearly stating that it received its first publication by Ehrenberg ( 1 849) , 

 credited the authorship to Deane, even after pointing out that "the name Arachnoidiscus 

 is carefully omitted from the account, thus robbing Deane of the recognition due to him " 

 (Brown, 1933, p. 13). Ralfs (in Pritchard, 1861) credited the name to Deane also. 



The type species was first described under Hemiptychus ornatus Ehrenberg (1848). 

 In the following year Ehrenberg changed the generic name to Arachnoidiscus upon a sug- 

 gestion put forward by Bailey, in correspondence, on the grounds that Hemiptycha had 

 been used as a generic name for insects. 



The use of a name for a genus of animals does not preclude it from use as a generic 

 name for plants, and upon that ruling it was quite unnecessary for Ehrenberg to 

 establish Arachnoidiscus. Mann (1907, pp. 266-7) stated that : " Ehrenberg's excuse for 

 abandoning his earlier name, Hemiptychus, is not valid As this first name of Ehren- 

 berg's is valid and his diagnosis is clear and his type species well defined, namely 

 H. ornatus, it must replace the better known and far more descriptive name invented by 

 Deane." Mann continued to describe three species under Hemiptychus. Some years 

 later Mann (1925) entirely retreated from that position, and in his Marine Diatoms of the 

 Philippine Islands stated that his work "involves the rejection of a few names, chiefly 

 generic ones, which appear earlier in print, but with verbal description or illustration, 

 or in some cases both, so meagre and unsatisfactory as to make it a safer plan to treat 

 them as nomina nuda, than to accept the alternative, to so amend and amplify them that 

 they will be distinctly marked off from other genera subsequently discovered. They 

 comprise chiefly the following, Hemiptychus, for the universally used Arachnoidiscus...." 

 Farther on he says: "lam glad to here note that this upsetting of classical and long- 

 established names on my part has not had the slightest influence on subsequent diatom 

 literature" (Mann, 1925, p. 9). 



I feel that this complete recantation is 'somewhat remarkable, and was due probably 

 to causes other than those mentioned by Mann. It must be noted that the excuses put 

 forward in the above quotation were not strictly true, particularly in the genus under 

 consideration, from two points of view. Firstly, according to Mann's own statement in 

 1907, the diagnosis of the genus Hemiptychus was quite clear, and the type species well 

 defined, and there was no case whatever for considering it as a nomen nudum, or for 

 attempting to amend or amplify either the generic or specific descriptions. Secondly, no 

 systematic literature of any account had appeared between the years 1907 and 1925 that 

 contained a description of the genus or any of its species, so it can scarcely be said that 



