No. 513] 



STAB-FISHES 



558 



there is great variation in the size of different individuals 

 of young starfishes of equal age, of the same species, de- 

 pendent on temperature and relative abundance of food. 

 But I know of no experiments or observations to connect 

 this with the number of congenital rays. 



Distribution 



A number of Arctic species occur in Bering Sea and 

 as far south as the Aleutian Islands, or somewhat farther. 

 Most of these are circumpolar, as Crossaster papposus, 

 Solaster endeca, Henric'm sanf/uii/olcuta, Ctenodisnts 

 crispatus, Asterias polaris, Asterias hyperborea (=A. 

 arctica Murd.), A. grcenlandica = A. cribraria St. and 

 others. 



Some Arctic species are peculiar to the north Pacific 

 side, so far as known, as Pterasterides aporus (Ludwig), 

 Tosia arctica Ver., Asterias polythela Ver., Allasterias 

 rathbuiii Verrill, Pteraster octaster Ver. 14 and others. 



But exclusive of the Arctic forms, the entire starfish 

 fauna of the coast, from the Aleutian Islands to San 

 Francisco, is peculiar to that coast, so far as I can de- 

 termine, and is rather sharply limited, both northward 

 and southward by temperatures only. Some species 15 

 are closely related to North Atlantic ones, and evidently 

 represent divergent groups derived from a common stock, 

 at no very remote period. However, the cases of greatest 

 interest are those of generic types peculiar to the fauna, 

 some of which have no near allies elsewhere. Among 

 such genera I may mention here a few examples : Pycono- 

 podia, with no near allies; Acantharchaster Ver., a very 

 isolated genus; Dermasterias, with a single species; Gly- 

 phaster Ver. (type Leptychaster anomalus Fisher), with 



