40 AMERICAN HYDROIDS. 



tematic value unless reenforced by the characters of the operculuna and hydrothecal margin, upon 

 which he chiefly relies in his system of clussilication. He iiiiiintains that, there is a constant 

 relation between these last two structures, and that the operculum is always attached to more or 

 less deepened curves or sinuosities of the margin. 



In accordance with this position, based, as the author expressly states, on his studies of the 

 Greenland species only, Professor Levinsen in another work published during the same year 

 (1SK3), 1 classifies the Sertularida 1 as follows: 



(a) Operculum of 3 or 4 Haps which aiv attached to a like number of emarginations of the walls of the hydrotheeir. 



Gonangia annulated f&rtubireltn. 



(a') Operculum of a single flap. 



(b) Margin of hydrotheca with two lateral teeth. 



(c) Ilydrothecfe in a single zigzag row. Operculum adcauline HijilrnlliiKiiiin. 



(c') Hydrothec;e in two rows. Operculum attached to adcauline side of margin ftertulnrin. 



(I)') Margin of hydrothecie without teeth. 



(c) Operculum attached to adcauline side of margin TUplmsin. 



(c') Opereulum attached to abcauline side of margin _ Tlniim-in. 



In applying this key to the large, number of species discussed in the present work it becomes 

 evident that it is inadequate to meet the requirements of the case, however well it applies to the 

 Greenland forms discussed by Levinsen. 



The scheme is so attractive at first sight that the writer must confess to a sense of personal 

 disappointment at the failure of a method of classification for which he sincerely desired success. 

 The following considerations, and several others could be added, are sufficient to show the 

 inadequacy of the key. 



In the genus XiTtuhnvUn the form S. formosa Fewkes (Plate XXVI 1, tig. 2), has an abso- 

 lutely even margin, and an operculum that, when present, is stretched like a drumhead over the 

 very wide operculum. The same, is true of 8. luii'tlnuli Nutting. I can not see how either of 

 these can be rightfully separated from the genus Sertula/rella. 



The hydrothecal margins in IlydritUuiunin can seldom be said to have two teeth, and indeed 

 are often perfectly oval, or with slight angulations at the sides that cannot properly be called 

 teeth in the sense in which the term is used in reference to the margins of hvdrotheca-. 



Mr. Paarmann, who has very carefully studied many species of sertularians that would come 

 under the genus Sertularia, according to the key given above (including A". /"/ m!t<i and other 

 long-known forms), by means of serial sections concludes that Professor Levinsen is incorrect in 

 saying that the operculum of this genus consists of a single flap. As this is a matter of 

 unusual importance I quote from his unpublished manuscript: 



In the species having bilabiate (bidentate) margins each of the emarginations is surmounted by a membranous 

 piece of (lie operculum. Levinsen (p. 187) says that the adcauline piece is permanently attached to the margins of 

 the teeth, thus forming a " collar," while the abcauline piece is a free functional flap which opens when the 

 hydranth expands and closes after the hydranth has retracted. Upon this type he bases his genus S< rtnliiria. The 

 investigation of a large number of specimens by means of longitudinal and cross sections shows that this condition is 

 by no means uniform. Sometimes the adcauline piece is attached while the other is free, and sometimes the reverse 

 is true. Often the sides of a flap are attached for a greater or less distance proximally while they become free 

 distally, the degree of attachment varying greatly even in the same species. In most cases both flaps are functional. 



I have examined Mr. Paarmann's sections and am convinced that the statements above quoted 

 are correct. Jt seems evident that Allman 2 and Marktanner-Turneretscher :t are correct in inter- 

 preting the hydrothecai of such species as Serfadww pumila as having a two-valved operculum. 4 

 This conclusion would make it necessary to fundamentally modify the table of classification pro- 

 posed by Levinsen. But there is still another and even greater objection to relying exclusively 



1 Annulata, Hydroidme, Anthozoa, Porifera in: Det videnskabelige Tdbyttc af Kaiioiibaascn "Hauchs" Togter, 

 Copenhagen, 1S93, pp. 321-425. 



- Memoirs of the Museum of Comparative Zoology, V, 1877, p. 25. 



' Hydroideii des k. k. naturhistorischen Hofmuseiims, Vienna, 1S90, p. 238. 



4 It seems to me that even by Levinsen's account the operciilum is here morphologically, although not function- 

 ally, two-valved, and that his so-called "collar" is, like the opcn-ulum, simply a thin membranous extension of the 

 hydrotheeal wall. See Meduser, Ctenophorer og Hydroider fra Gronlands Vestkyst, 1SSI3, p. ISO et </. 



