SYSTEMATIC ACCOUNT 325 



It is fairly common in temperate and in tropical waters, particularly in the Mediter- 

 ranean and the Indian Ocean. 

 Observed at Sts. 425, 433. 



Family CORETHRONACEAE 



Subfamily CORETHRONOIDEAE 



1. Cells cylindrical, straight, valves furnished with circlet of long bristles directed towards the 

 same pole, secondary corona of hairs bearing claws often present ... ... Corethron 



Genus Corethron Castracane 

 Castracane, 1886 



The genus Corethron has received considerable attention of late, and most plankton 

 workers are convinced of the close relationship that exists between the so-called species. 

 I have expressed my own views on this subject on p. 216 and merely state here that I am 

 confirmed in my belief of the specific unity of all the described forms. This monotypic 

 genus presents a perfect example of what I mean by a polyphasic species-system, and 

 can only be understood correctly if the species is conceived as an orbital system in a 

 space-time continuum. 



Under the name of the type-species I include all the described forms, and for the 

 purpose of this paper, recognize five phases. The phases are not at all clear and the 

 overlapping that occurs makes definition extremely difficult. 



Corethron criophilum Castracane. 



Castracane, 1886, p. 85, pi. 21, fig. 14. 

 Corethron valdiviae Karsten, 1905, p. 101, pi. 12, figs. 1-10. 

 Corethron hystrix Hensen, 1887, p. 89, pi. 5, fig. 49. 

 Corethron inerme Karsten, 1905, p. 104, pi. 13, figs. 11-17. 

 Corethron Murrayanum Castracane, 1886, p. 86, pi. 21, fig. 4. 

 Corethron pelagicum Brun, 1891, p. 20, pi. 19, fig. 6. 

 Corethron hispidum Castracane, 1886. 



Under the name Corethron criophilum, I place as synonyms all the described forms. 

 The large and plastic Corethron population, however, cannot be adequately described 

 under any one name, but any attempt to arrange the names quoted above with a view to 

 ascribing rank, subspecific or otherwise, would be very difficult. The acceptance of the 

 orbital conception of a polyphasic species-system makes subspecific ranks unnecessary, 

 and the following method of description does not attempt in any way to place in order 

 of importance or to grant status or rank of any kind to the various phases, which have 

 been chosen solely upon the ground that they portray adequately the Corethron popula- 

 tion under consideration. 



The following description has been framed to cover all the phases observed in the 

 'Discovery' material. 



