316 RHODALIIDAE. 



The determination in Dromalia, and in well-preserved material of Archan- 

 gelopsis, that aurophore and zone of proliferation lie upon opposite sides of 

 the corm, is gratifyingly easy; and to find a satisfactory explanation for this 

 phenomenon is not so difficult at it appears at first. It is true that we are 

 once more face to face with the anomaly experienced by Chun, from which Lens 

 and Van Riemsdijk tried to escape, that while in Physophora the pneumatochone 

 with its enclosed portion of the gastro vascular space is ventral, in Rhodaliidae 

 the organ which exactly corresponds to it is as certainly dorsal. The explana- 

 tion, as already suggested (p. 269), is that Physophora is not the parent of the 

 Rhodaliidae, but that both are descended from members of the Agalmid stock. 

 And in the Agalmidae, as is well known, the primitive pneumatochone is neither 

 dorsal nor ventral, but axial. Even in the highly specialized genus Nectalia 

 this is the case, and it is also true of Anthophysa, in which the pneumatochone 

 organ may be supposed to have undergone regressive changes. 



For light on this question we must await renewed researches on more exten- 

 sive material. Especially desirable would be a knowledge of the very young 

 stages of any one of the Rhodaliidae; but of these we yet know practically 

 nothing, because Haeckel's ('88b) account of his "Auronula" larva was so 

 superficial and based on such a fragmentary specimen that it is of little value. 



Distribution of the Rhodaliidae. Stephalia is recorded from the eastern 

 part of the Gulf Stream, from the Faroe Channel and Shetland Islands, and 

 Stephonaha from the South Pacific; west of New Zealand, lat. 38° 50' S., 

 long. 69° 20' E. (Haeckel); Angelopsis, from the Gulf Stream (Fewkes), from 

 the Tropical Atlantic (Haeckel) and Tropical Eastern Pacific ("Albatross"); 

 Rhodalia, from the South Atlantic, 37° 17' S., 53° 52' W. (Haeckel), and prob- 

 ably from the Tropical Pacific in the neighborhood of the Galapagos (Brooks 

 and Conklin, '91); Archangelopsis, from the Malaysian region ("Siboga") and 

 from the northwest Pacific ("Albatross"). 



Respecting the bathymetric range of the Rhodaliidae I may point out that 

 all the hauls from which they have been recorded were made with open nets 

 and therefore afford no real clue to the depths from which the specimens in 

 question came. That they are not such good evidence of abyssal habitat as 

 Haeckel supposed is indicated by the fact that the "Siboga" specimens of 

 Archangelopsis were taken within 100 and 112 m. of the surface. Moreover 

 Fewkes ('89a), and more recently Lens and Van Riemsdijk have given strong 

 reasons for believing that the extraordinary development of the pneumatophore 

 suggests a habitat near the surface, rather than at great depths. 



