Howe: Phvcological studies 501 



C. On the American species of the Mai.imeda tkioens 



GROUP 



P>en before writing " Phycological studies — II," * in which we 

 described Halimcda favulosa as a new species and followed Mrs. 

 Gepp (Ethel S. Barton) and also Harvey in considering Halimcda 

 Mouilc (VAX. & Soland.) Lamour. a mere variety or form, we had 

 seen both Halimcda tridcns f (//. incrassata) and //, Monilc grow- 

 ing in close proximity to each other in Bermuda, in Porto Rico, 

 and in the Bahamas, and remaining apparently distinct. But the 

 segments in both of these were subject to so much variation in 

 outward form, even in different parts of a single individual, that 

 plants from other localities would sometimes appear to occupy an 

 intermediate position, and great as were the manifest differences 

 between the best representatives of these two types it seemed diffi- 

 cult to draw any satisfactory line between them. When, however, 

 in December, 1906, and Januaiy, 1907, we again saw, in several 

 localities in Jamaica, Halimeda tridcns and H. Monilc growing 

 either side by side or within a few feet of each other and always 

 maintaining their distinctive characters perfectly, the conviction 

 was forced upon us that a mistake had been made in considering 



*Bull. Torrey Club 32 : 563-586. //. 23-2g. 1905. 



f One who has seen an extensive series of West Indian Ilalimedas, either growing 

 or in an herbarium, can scarcely have any serious doubts, we believe, as to the intended 

 application of Ellis & Solander's names Corallina tridens and Corallina incrassata or 

 as to the impossibility of drawing any reliable line of specific separation between the 

 two. This being granted, the next question involves a choice between the two names, 

 published in one work at the same time. Mrs. Gepp, in her monograph of "The 

 Genus Ilalimeda" (Siboga-Exped. LX) has adopted the specific name incrassata, 

 presumably because Ellis & Solander's description of their Corallina incrassata was 

 accompanied by the more numerous and more detailed figures. The Rochester and 

 the Philadelphia codes of botanical nomenclature give preference in such cases to the 

 name having "precedence of position," which would here call for the adoption of the 

 specific name tridens, the name which, fortunately, in America, at least, has been the 

 more generally employed. The recent Vienna Code (Art. 46) provides that " when 

 two or more groups of the same nature are united, the name of the oldest is retained. 

 If the names are of the same date, the author chooses, and his choice cannot be modi- 

 fied by subsequent authors." In the case in hand, technical priority in the matter of 

 publishing a choice between the two names appears to lie, by a narrow margin, so far 

 as we can discover, with Mr. F. S. Collins, whose choice of Halimeda tridens appeared 

 in print in November, 1901 (Proc. Am. Acad. Arts and .Sci. 37: 246) while Mrs. 

 Gepp's monograph, in which the name Halimeda incrassata is preferred, bears the date 

 of December, 1901. 



