THE SPECIES OF lOPHON 349 



the north, a more speciaHzed species has sprung (/. piceus). To the south, it has given 

 rise to /. proximum, again a sHghtly more speciaHzed species, but one in a state of extreme 

 fluctuation as regards its spicular characters (cf. Figs. 22-24). From this variable species 

 have arisen several more speciaHzed species, which have migrated in a southerly 

 direction: /. laminalis in the Southern Ocean, /. omnivonis in AustraHa, /. laevistyliis 

 in New Zealand, and /. radiatus in the Antarctic. At the northern limit of its range 

 of distribution, it has possibly given rise to another speciaHzed species, /. melanokhemia. 



We have here an indication that the species of lophon have developed from a form 

 the prototype of which is located in the North Atlantic, and that its most specialized 

 species is found in the Antarctic. The same thing may be said of the species of Mycale. 

 In point of numbers, the species of the North Atlantic (i.e. on the European side) are 

 the most numerous. Elsewhere the species of this genus are found mainly in the 

 Antarctic and sub-Antarctic, and in the Indo-Australian area ; but whereas the Indo- 

 Australian species are either Httle more specialized than those of the North Atlantic, or, 

 more commonly, degenerate (cf. ArenochaUim mirabilis, Lendenfeld, from Australia, a 

 degenerate Mycale), the Antarctic species are somewhat more specialized than any of 

 the rest. Moreover it may be noted that the six Antarctic species of Mycale are found 

 in localities bordering on the area of distribution of M. magellanica (Ridley), a species 

 comparable with lophon proximum (Ridley) in the variability of its spiculation. Finally, 

 we find that the two most specialized species of Mycale, M. intermedia, Schmidt, and 

 M. acerata, Kirkpatrick, are found in the Arctic and Antarctic respectively. 



The distribution of the genus Amphilectiis is also similar to that of lophon and 

 Mycale. The least specialized and most variable species, Amphilectus fiicorum (Johns- 

 ton), is distributed generally around the European coasts and in the Arctic, is found 

 on the west coast of Africa, around the southern extremity of South America, in the 

 Antarctic, and finally at New Zealand. Again we find specialized species, A. qiiatsi- 

 noensis (Lambe), on the west coast of Canada, and A. americana (Ridley and Dendy) 

 around the southern extremity of South America. In addition, there are Corybas lobata 

 (Johnston) in the North Atlantic and Arctic, and Brondstedia glaber (Br0ndsted) in 

 the Antarctic, both of which must be regarded as species closely related to Amphilectus 

 fucorum but slightly more specialized. 



The genus Isodictya is confined practically to the Arctic, European coasts, south 

 coast of Africa, southern extremity of South America, the Antarctic and New Zealand. 

 And again we find the most primitive species in European waters, while around South 

 Africa the species of this genus show a rich development in numbers of species, size 

 of individuals and growth of spicules. This progressive tendency in the South African 

 species of Isodictya is carried still farther in the sub-Antarctic and Antarctic, where the 

 genus reaches its highest degree of development. 



There is in this a striking parallel which cannot be ignored, and which suggests that 

 four of the most primitive sections of the Desmacidonidae — the Isodictyeae, the Myca- 

 leae, the Tedanieae and the lophoneae — have each arisen in an area approximating to the 

 European side of the North Atlantic, and from thence have spread northwards to the 



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