SHALLOW-WATER STARFISHES 19 



2d. Those that are of Arctic or circumpolar distribution and 

 extend southward into Bering Sea, and in many cases to the Aleutian 

 Islands, or much farther south, especially in the deeper waters. 

 Their origin may have been in the North Pacific originally, in many 

 cases. 



3d. Those that appear to have originated in the region extending 

 from the Aleutian Islands to California. 



The last group is by far the larger and more important. Very 

 likely it is possible to divide that very extensive coast line into two or 

 more faunal districts, but for the starfishes this does not seem 

 to be necessary for the present, for many species range throughout 

 that whole extent of coast. 



The limits of distribution on that coast seem to be determined 

 entirely by the temperature of the water, especially in the breeding 

 season, due probably to the greater sensitiveness of the free-swim- 

 ming larval forms. The adults can regulate their temperatures by 

 migrating into deeper or shallower water as occasions require. 



Among the more southern forms are Orthasterias forreri, Pisaster 

 capitatus, P. paucispinus, Marthasterias sertulifera, species of Astro- 

 pecten and Luidia, Linckia Columbia, etc. 



Among the arctic and in part circumpolar species are Asterias 

 acervata, A. multiclava, L. arctica, C. cribraria, Allasterias rathbuni, 

 Henricia sanguinolenta, H. tumida, H. arctica, Solaster endeca, 

 Crossaster papposus, Pteraster obscurus, and var. octaster, P. mili- 

 taris, Diplopteraster multipes, Tosiaster arcticus, C. granularis, 

 Leptychaster arcticus, Ctenodiscus crispatus, etc. 



The species apparently indigenous on that coast are too numerous 

 to enumerate here. Some of them are nearly allied to those of the 

 North Atlantic and other regions, but many are very peculiar and 

 have no near allies in other regions, so far as known. 



A number of the genera and higher groups are peculiar to that 

 coast, others have there a remarkable development in number and 

 variety of species, showing that their evolution must have gone 

 along continuously for vast periods of time. In many cases primi- 

 tive and highly specialized species of a family are found associated. 

 Among these peculiar types are Pycnopodia, Rathbunaster, several 

 species of Pisaster, many species of Asteriinae, Dermasterias imbri- 

 cata, Leptychaster (Glyphaster) anomalus, Pteraster tesselatus, 

 Bunodaster ritteri, etc. 



Fuller lists will be given at the end of this work, with more 

 details of their distribution. 



