REPORT ON THE SIPHONOPHOR^. 71 



conectas, or all the " Medusae chondrophoras " of Chanrisso and Eysseuhardt. After- 

 wards (in 1835) Brandt separated the true Velellidas (with elliptical disc and vertical 

 crest) from ' the Porpitidas (with circular disc, without crest). The Velellidas, thus 

 restricted, agree with the Porpitidas in the polygastric structure, not only the large 

 sterile central siphon possessing an open mouth at its distal end, but also each of the 

 surrounding gonostyles. These peripheral polypites, which bear the gonophores budding 

 from then proximal part, are therefore not mouthless palpous (as in the Discalidse), but 

 mouth-bearing, feeding, and digesting secondary siphons. On the other hand, the Velellidas 

 differ from the Porpitidas (as well as from the Disealidas) in the peculiar amphithect or 

 bilaterally-radial ground-form of the body, produced by the prolongation of the sagittal 

 axis, and shortening of the frontal axis ; and, further, in the development of a peculiar 

 vertical crest or sail, which arises from the exumbrella either in the sagittal or in a 

 diagonal axis. 



Eschscholtz, in his fundamental work, 1 divided his Velellidas into three genera : — 

 Rataria, Velella, and Porpita. The genus Rataria, however, was considered by the ma- 

 jority of subsequent observers to consist only of young forms of Velella. A new species of 

 Rataria, found in the Challenger collection, proved to be an autonomous genus, provided 

 with gonophores. Although the different Ratarise, described by some authors, may be 

 merely young Velella}, there nevertheless exist also Velellidas which become mature in 

 the permanent i2atan'a-form. The numerous species of the true Velella were disposed 

 in my System (p. 31) in two genera : — Velella (sensu restricto), with an elliptical 

 umbrella and simple corona of tentacles; and Velaria, with quadrangular umbrella and 

 double or multiple corona of tentacles. For this latter the old name Armenista (or 

 Armenistarium of Carburius, 1757) may be better retained. 



Umbrella. — The common trunk of the cormus, which corresponds to the umbrella of 

 a hydromedusoid person, is in all Velellidse a flat, horizontally expanded, and floating 

 disc, distinguished from the circular disc of the Porpitidas and Disealidse, firstly, by 

 its bilateral form, and secondly, by the vertical crest or sail. The latter is originally 

 nothing more than a simple longitudinal fold of the exumbrella, and may be regarded 

 as the primary cause of the peculiar fundamental form. The three genera which we 

 have distinguished represent three different degrees or historical steps in its peculiar 

 development : — Rataria, next to the ancestral group Porpitidas, has an elliptical disc, and 

 the sail placed in its sagittal plane, in the longer axis ; in Velella the sail turns a little 

 around the vertical main axis, and comes to be situated in a diagonal axis of the disc ; 

 finally, in Armenista the disc becomes quadrangular or parallelogram-shaped. Besides, 

 a vertical crest of the pneumatocyst, as a support of the soft sail, is developed in the two 

 latter genera, but is wanting in Rataria. 



Amphithect Fundamental Form. — The peculiar fundamental form presented by the 



1 1, 1829, p. 166. 



