-^(5 BULLETIN 16, UNITED STATES NATIONAL MUSEUM. 



Variations. —Certam variations due to size are shown in the following table: 

 Table showing variations in Psilaster pectinatus. 



The greater number of sjiecimens examined are from Bering Sea. Among 

 these the chief variations are in ])roportions, including length and width of ray 

 relative to disk; in the amount of inflation of abactinal integument; relative size 

 of ei)iproctal elevation; number of superomargmal spLnules; the degree which the 

 exposed surface of marginal plates, or in other words the side wall of ray, departs 

 from the perpendicular; adambulacral spinelets of furrow series are seven or eight; 

 shght difference in size of actinal interradial areas; the tenuity of extremity of 

 rays; compactness of actinal intermediate paxillse. There is also a trifling varia- 

 tion in the size of paxillae of abactinal area; as a whole the specimens are remark- 

 ably uniform in this character. 



Unfortunately there are only three adult specimens from off southern Cali- 

 fornia. These are pretty much alike. One specimen has a narrower paxillar 

 area on rays, but a larger disk and larger paxillse than have the other two. Com- 

 pared with specimens from Bering Sea, these examples present no important dif- 

 ferences. The rays are a trifle thicker dorsoventrally, and the sides are a little 

 higher ia consequence. The marginal plates are more vertical in the southern 

 specimens than in those from Bering Sea, where the side wall of ray generally 

 slopes inward on the actinal surface. But many from the latter locality have 

 the side wall nearly vertical. There are not enough southern specimens to deter- 

 mine whether the presenc^e of a second superomarginal spinule is more frequent 

 in the northern individuals. The marginal spinules sometmies stand out at an 

 angle from ray, but are more often tightly appressed to side; this difference changes 

 the general facies in a misleading manner. Smaller specimens as a rule have the 

 rays thicker near the tips than the large examples. 



All the variations ajjpear to be of slight importance — that is, are such as may 

 be expected in starfish S])ecics — and the Alaskan examples belong, seemingly, to 

 the same species as the California sjiecimens. The latter show no important dif- 

 ferences from Panamic examples described by Ludwig under the name Plutonaster 

 abyssicola. 



Young. — Young examples have much shorter, blunter, and distally thicker 

 rays than adults and half-grown specimens, the difference in proportions having 

 been given in the foregoing table. The marginal plates are more prominent on 

 the abactinal surface; each plate of both series (except near tip of ray of supero- 

 marginal series) bears a single spinule. The adambulacral plates liave five to 



