368 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



Pedicellaster, Leptasterias, Asterias, or in other p;roups having constantly six-rayed 

 species. In the absence of any structural features separating this form from 

 Pteraster, I have classified the species under that genus. 



Since the above was written Professor Verrill has described Pteraster octaster 

 from Bering Island." I have listed two specimens with eight rays from Bering 

 Island, evidently a part of the same lot collected by Doctor Stejneger. These are in 

 rather poor condition as regards the actinal surface, but a small specinien from 

 station 3557 is in a perfect state of preservation. 



I have gone over these specimens again and have compared them with seven- 

 raj'ed and sLx-rayed examples. The result is that I am unable to find sufficient 

 structural difference to warrant the segregation of the eight-rayed form as a sepa- 

 rate species. The highly characteristic paxillse are the same in the eight as in the 

 six- and seven-rayed specimens, showing no more variation than can be found in 

 several six-rayed examples. So also with the actinal surface. In eight-rayed 

 specunens the interradial areas are naturally smaller than in examples with six 

 rays, but not much smaller. The structure and spinulation of the mouth and 

 adambulacral plates is the same. 



Reference has already been made to the fact that the young of the large seven- 

 rayed specimen have six rays. I opened the nidamental cavity of the two eight- 

 rayed Bering Island examples and found six young, one of which has nine rays, 

 three have eight rays, and two have seven rays, all three kinds being found in the 

 same individual. This is enough to show that there is no stability in the number 

 of rays. This circumstance coupled with the structural similarity of six-, seven-j 

 and eight-rayed specimens has led me to place Pteraster octaster as a synonym of 

 obscurus. 



It is of interest to note that Professor Verrill described the new form as a 

 Pteraster and not as Hexaster ( Temnaster Verrill) . 



Two specimens were opened, but were too badly macerated to determine the 

 internal stnicture in detail. The anatomy seems to be essentially the same as 

 in typical Pteraster. 



In "Some Japanese and East Indian Echinoderms " '' Dr. Hubert Lyman 

 Clark has published a very useful key to the species of Pteraster, upon wliich the 

 following key is based. Pt. aporus has been omitted, and a number of changes, other 

 than the introduction of new species, instituted. As the two keys differ in some 

 details, both may be used to advantage for the identification of specimens. The 

 key has been brought up to January, 1910. 



KEY TO THE KNOWN SPECIES OF PTERASTER. 



a'. Form more or less stellate; R greater than 1.8 r, usually 2 to 3.5 r. 

 b'. A stout spine (suboral) present on surface of each mouth plate, 

 c'. Tube feet in two series; supradorsal membrane with spiny deposits^ and not conspicuously 

 reticulated. 

 cP. Ambulacral comb with more than five spines. 



e'. Stalk of paxilla short, not much higher than thick; spineleta much longer, three to five; 

 supradorsal membrane crowded with deposits; oral spines six to eight, .militaris, Miiller. 



"Amer. Joum. Sci., July, 1909, p. 61, fig. 1. 



6 Bull. Mus. Comp. Zool.. vol. 51, No. 11, April, 1908, p. 286. 



c Not mentioned in caribbxus and affinis; probably present. 



