348 DISCOVERY REPORTS 



THE EVOLUTION OF THE SPECIES OF lOPHON, 



AND ITS SIGNIFICANCE IN RELATION TO OTHER 



ANTARCTIC SPECIES OF ECTYONINAE 



The genus loplion provides another striking plan of the distribution of species and, 

 in addition, a probable indication as to the generation of species. In the North Atlantic, 

 restricted to the coasts of the Mediterranean, and of Western Europe as far north as the 

 British Isles, are two species, closely allied and apparently the most primitive of the 

 genus. These are /. pattersoni (Bowerbank) and /. hyiidmaui (Bowerbank). It is a re- 

 markable fact that these two species are almost invariably found growing in association. 

 That is to say, if, in a single haul of the dredge, examples of one species are obtained, 

 examples of the second will almost certainly be present also. There is yet a third species, 

 /. scandens (Bowerbank), of rare occurrence, the characters of which are intermediate 

 between those of the other two species. It appears probable that future research may 

 show either: (i) that these three species represent different growth stages of a single 

 species; (ii) that /. pattersoni and 7. hyndmani are forms of a single dimorphic species, 

 and I. scandens an occasional intermediate; or (iii) that /. pattersoni and I. hyndmani 

 are distinct species, and possibly I. scandetis a hybrid. At all events, it will be convenient 

 to regard them here as representing a single primitive species. 



The remaining six species of the genus are all more specialized than the foregoing in 

 many respects, especially in their external form and in the shape of the bipocilla. The 

 first of these is I. piceus^ (Vosmaer), found on the coasts of Norway and in the Arctic. 

 The second is I.proximum (Ridley), which is found throughout the sub-Antarctic, from 

 Kerguelen (and Natal) to South America, up the western coast of South America to 

 the Galapagos, on the we'^tern coast of North America and possibly round to the eastern 

 coast of Canada. In addition, it is found rarely in the Antarctic. The third species, 7. 

 laminalis, Ridley and Dendy, from Prince Edward Island, is closely related to, if not 

 synonymous with, 7. proximmn. The fourth, 7. omnivorns, Ridley and Dendy, from 

 Australia, is slightly degenerate, though still somewhat more specialized. The fifth, 

 7. laevistyliis," from New Zealand, is more specialized. The sixth, 7. melanokhemia (de 

 Laubenfels) from Puget Sound, is probably also a specialized offshoot from 7. proxi- 

 mim. The last, and most specialized, 7. radiatns, Topsent, though also found in the 

 Falkland Islands area of the sub-Antarctic, is most numerous in the Antarctic proper. 

 This species, in its development, passes at first through a stage recaUing the hyndmani- 

 pattersoni group, and, later, shows certain features associated with 7. proximum. 



The picture (Fig. 45) presented by these species may be summarized as follows. The 

 group represented by 7. hyndmani and 7. pattersoni is a primitive one, and from it, to 



1 There can be little doubt, in view of the variability of the spicules found in /. radiatus and /. proximum, 

 that I. piceus, Vosmaer, I.frigidus (Levinsen) and /. dubius (Hansen) are conspecific ; especially as they are so 

 alike in external form. 



' lophon major and var. lemiis, Brondsted, and /. minor, Brondsted, are quite evidently conspecific with 

 /. laevistylus, Dendy, in view of what is now known concerning the variations in all species of lophon. 



