ECOLOGY AND TAXONOMY OF Halimcda 31 



This use of additional microscopic characters represents an im- 

 portant refinement of taxonomic criteria for the genus and an early 

 application of field experience with this taxon, which Barton and most 

 of the preceding workers on Halimeda did not have. Howe appears to 

 have been provoked into looking for reliable differences in microscopic 

 structure because he had observed incrassata (his tridens), and monile 

 growing in close proximity in Bermuda, Puerto Rico and the Bahamas, 

 yet remaining distinct. Where simulans was observed growing near 

 incrassata he also reported no intergrading forms (Howe, 1907). This 

 character remains one of the most useful microscopic criteria for 

 separating species of Halimeda. 



Howe (1907) also suggested changes in nomenclature to take 

 account of apparent priority of species authorship. He renamed 

 incrassata with the epithet tridens, which he believed had priority. 

 Barton had chosen the epithet incrassata when merging older species, 

 but Collins (1901), whose "Algae of Jamaica" preceded Barton's 

 monograph by a few months, had chosen tridens for a similar merger. 

 Howe's decision depended on Collins having correctly identified the 

 type description of incrassata and tridens as being that referred to in a 

 single publication by Ellis and Solander (1786). The first author to 

 merge species erected in a single earlier paper has priority of choice for 

 the name to be used (International Rules of Nomenclature). Collins 

 chose tridens; Barton chose incrassata; Collins chose first. 



Borgesen (1911, 1913) put the merged species back to incrassata 

 where Barton put it. This argument over naming the species has had 

 the heritage that American and European workers gave the same 

 species different names for much of this century. Americans followed 

 Howe in using tridens and Europeans followed Borgesen and Barton in 

 using incrassata. This confusion was only resolved with the monograph 

 of Hillis (1959). In this it was demonstrated that incrassata is the 

 appropriate name because Ellis, in his 1767 publication, included 

 excellent illustrations, with analyses, of a "coralline" to which he 

 applied the specific epithet ''incrassata'' (Fig. 12). This meets the 

 requirements for valid publication as stated in the Paris Code (Lanjouw 

 et al., 1956, Article 43). The original merger proposed by both Collins 

 and Barton is still accepted, and the name of the species is Halimeda 

 incrassata and not H. tridens. 



Borgesen's (1911, 1913) interpretation of Caribbean material tended 

 to parallel Howe's, yet refiected his own thinking. He considered that 

 monile and simulans differed sufficiently from incrassata to be treated 

 as separate taxa, but that they were only varieties of incrassata. These 

 subspecies were considered of specific rank by Hillis (1959), as originally 



