CTENOPHORA. 69 



as "die eiformige, rosenrotgefarbte Plcitrobrachia rhodopis ", this somewhat increased colouring being 



evidently due to a lapsus memorise of Dr. Moser. 



These distinguishing characters certainly seem quite excellent. Finding, however, that the 

 young specimens of PI. pileus were not easily distinguished from PI. rhodopis after the diagnosis given, 

 I asked for some material of rhodopis from the Zoological Station at Naples. I was then rather sur- 

 prised in finding that these specimens did not correspond very well with the diagnosis of rhodopis ; 

 especially the opening of the tentacle-basis was not at the level of the infundibulum, biit placed as in 

 PL pileus of a corresponding size. After a careful comparison with specimens of pileus from the North 

 Sea I became convinced that it is impossible to distinguish the two forms. The characters 

 pointed out as distinguishing PL rhodopis from pileus are only characters of the young, 

 found exactly alike in specimens from the Mediterranean and the North Sea. It is in correspon- 

 dance herewith that the specimens examined by Chun were only 5 7 mm . In the preserved specimens 

 I find the opening of the tentacle sheath lying at the level of the infundibulum at a size of 3 4 mm , 

 while in specimens of 5 7 mm it is already somewhat more apically placed. This difference evidently 

 is due to the preservation, the size of the animals being more or less reduced thereby. 



Another fact is decidedly in favour of the identity of PL rhodopis and pileus, viz. that while 

 PL pileus has otherwise an almost cosmopolitan distribution, it is not known from the Mediterranean '), 

 doubtless because the specimens found there are eo ipso taken to be rhodopis, which latter has, on the 

 other hand, not been recorded from outside the Mediterranean. The improbability of such a world-wide 

 pelagic form not occurring in the Mediterranean is evidently as great as that of another similar 

 pelagic form not occurring outside the Mediterranean. 



The identity of rhodopis and pileus, on the other hand, would seem to be disproved by the 

 observations of Gar be 2 ), who has found very considerable anatomical differences between the young of 

 the two forms. In the youngest specimens of PL rhodopis examined, 0-5 mm in diameter (collected at Triest), 

 the gastrovascular system was as yet very little differentiated, being represented only by a large, undi- 

 vided sac in each side half of the body; in young specimens of PL pileus from Helgoland, of only O'4 mn1 

 diameter the gastrovascular system was found almost completely formed as in the grown specimens. Also 

 in regard to the development of the genital organs very considerable differences were found to exist 

 between the two species, which need not be recorded in a more detailed way here. It is, of course, 

 beyond doubt that such two forms could not be identical --on the contrary, the differences found by 

 Gar be are so considerable, that it seems really astonishing that such could obtain in two species of 

 the same genus. The explanation of the remarkable discrepancy between Garbe's and my own 



") Moser (Op. cit. p. 145) doubts the correctness of a statement of Sovinsky, according to which PI. pileus occurs 

 in the Black Sea. As I have not seen Sovinsky's work ("Einfuhrung in das Studium der Fauna des Ponte Caspo, aral. Meeres- 

 Bassin". 1902), I can form no judgment of the case, but it would beforehand seem very probable that the Mediterranean 

 Pleurobrachia, which is really PI. pileus, also occurs in the Black Sea, corresponding to the fact that it occurs also in the Baltic. 

 - When Moser further says that "es ware wertvoll, zu erfahren . . . welche Art unter dem Namen Pleurobrachia rhododactyla 

 gemeint ist, die nach Graeffes kurzer Mitteilung (1884) ini Golf von Triest haufiger ist; dass es sich hier um unsere nordische 

 Pleurobrachia pileus handeln sollte, lasst sich kautn annehmen bei dem Fehlen anderer nordischer Arten wie z. B. Beroe citcumis", 

 it must be stated, firstly, that Graeffe ("Ubersicht der Seethierfauna d. Golfesv. Triest. III. Coelenteraten. 1884. p. 30) mentions 

 PI. rhodopis, not PL rhododactyla, and next that the Mediterranean Beroc ovata is doubtless identical with Beroe cucumis, which gen- 

 erally occurs together with PI. pileus. (Comp. below, sub Beroc cucttmis). 



') Aug. Garbe. Untersuchungen iiber die Entstehung der Geschlechtsorgane bei den Ctenophoren. Z. wiss. Zool. 

 Bd. LXIX. 1901. 



