Chap. II. CTENOPHORiE SACCATiE. 195 



Cydippe of Esclischoltz Cydippid.e, and at -the same time pointed out two groups 

 among these Acalephs, which seem to me to constitute in reaUty two distinct 

 families. To one of these groups he refers the compressed species, of which the 

 Eschscholtzia cordata of Kolhker is the type ; to the other, he refers the more 

 rounded species, of which the Cydippe Pileus of Eschscholtz is the type. But, in 

 enumerating the species wdiich he would associate with the latter, he mentions 

 those wdiich are quite as remarkal^le for their compressed form as the Eschscholtzia 

 cordata. We have therefore to make a preliminary survey of the whole group 

 before we can proceed any further in characterizing this family. It is obvious 

 that when Eschscholtz characterized the genus Cydippe he had chiefly round or 

 oval species in view, the only ones belonging to this type he ever saw. It is, 

 further, unquestionaljle that his genus Cydippe is synonymous Avith Pleuroln-achia 

 of Fleming, and that, since Pleurobrachia is the older name, it must be retained. 

 The plea entered by Eschscholtz for discarding it, rests on a mistake : Fleming 

 did not call his genus Pleurobrancha^a, but Pleuroljrachia, on account of its lateral 

 arms, and it can never be confounded with Pleurobranchtea, so named on account 

 of its lateral gills. The name Cydippe must therefore be dropped as a generic 

 name, though there is no objection to retaining it as a family name. The genus 

 Mertensia Lcss.^ which Gegenbaiir would suppress, is a good genus, as remarkable 

 for its lateral compression as Eschscholtzia cordata, and therefore not belonging 

 strictly to the type of Cydippe. The genus Eschscholtzia Less, was established 

 for round species. It was therefore a mistake on the part of Kolliker to refer 

 his Eschscholtzia cordata to it. We shall see hereafter, that the genus Janira 

 OJcen also contains oval species l^elonging to the Cydippida3 proper, and that several 

 other species, referred either to Eschscholtzia or Cydippe, constitute also distinct 

 genera of that family. 



What I have already said is sufficient to show that Gegenbaur was on the 



^ Lesson has made a singular mistake in naming type of wliich was first observed by H. Martens, 



tliis genus, wliich he intended to dedicate to the and described by the latter under the name of 



oldest observer of the species he regards as its Beroe oetoptera. It is much to be regretted that 



type. Now, the oldest observer of this arctic Gegenbaur should have overlooked the claims of 



Acaleph is not II. Mertens, the naturalist of the Mertensia Less, to a distinction as genus, and on 



Russian exploring expedition in the Seuiavin, but that account proposed to transfer the name Mer- 



Friderich Martens, of Hamburg, the precursor of tensia to another type. But this cannot be done, 



Scoresby in the exploration of the seas of Green- not only because the genus Mertensia Less, must 



land and Spitzbergen, whose work was printed in stand, but also because the transfer of one generic 



1675, and whom Lesson quotes again and again name to another genus, even when that name has 



as Mertens. I shall therefore make good the mistake become vacant, leads to confusion, instead of simpli- 



of Lesson, and compensate for his error, by calling fying our scientific nomenclature. The rule I insist 



another genus of the same family Marteusia, the upon here is of long standing. 



