SHALLOW- WATER STARFISHES 13 



All the known species of these three remarkable genera are from 

 the Pacific coast of America and the outlying islands. 1 



Their resemblance to certain fossil starfishes of the Devonian is 

 very striking, and may indicate a continuous descent from those 

 ancient forms. If so, it would be good proof of the antiquity of the 

 West Coast forms, as mentioned above. 



Aside from these remarkable and localized genera, there are other 

 genera of the fauna that have numerous rays. The genus Solaster 

 is represented there by five or six shallow-water species, and 

 Crossaster by one. All these are multiple-rayed, the rays varying 

 from eight to fifteen. In these genera, there is no evidence of the 

 interpolation of new rays in post-larval life. They are also genera 

 that are widely distributed in all seas. (See pis. viu and x.) 



They appear to be more numerous on the Northwest Coast than 

 elsewhere, both as to individuals and species. Several additional 

 species occur in deeper water off the coast. The group may have 

 originated in the North Pacific, in former geologic ages. 



The genus Pteraster in all other seas has five rays, except 

 P. obscurus, of the North Atlantic and Arctic, which ordinarily has 

 six or seven. Variety octaster V., of Bering Sea, normally has eight 

 rays, but sometimes seven. Mr. Fisher thinks that it is only a variety 

 of P. obscurus, but even if so, it is singular that the latter should be 

 six-rayed in the Atlantic and anywhere from six-rayed to eight- 

 rayed in the North Pacific. 



So, likewise, other genera that are generally five-rayed in all other 

 parts of the world are apt to have six-rayed species on the North 

 Pacific coast. This is true of the genus Asterias and its subdivisions, 

 in which we find many six-rayed species on that coast, as well as 

 numerous five-rayed ones. Some of those that are ordinarily five- 

 rayed are also often found with six or seven rays. This occurs 

 in other regions, but not so frequently as there. 



Among the species of Asteriidae having normally six or more 

 rays, the following may be mentioned : Pisaster grandis (St.), a very 

 large species; Orthasterias merrianti V. ; A. acervata St.; A. kath- 

 erince Gray ; A. multiclava V. ; Stenasterias macropora V. ; Leptas- 

 terias hexactis (St.) ; L. vancouveri (Per.) ; L. aqualis (St.) ; L. 

 coei V. ; L. epichlora (Br.), subsp. alaskensis V., and several varie- 

 ties of the same species; and L. macouni V. 



Some of these have occurred with seven rays, and some with five, 

 as abnormal variations. 



1 Two species of Heliaster occur at the Galapagos Islands, and one at Juan 

 Fernandez. These were evidently derived from Pacific coast ancestors. 



