76 



B1 l.l.ETIN 76, UNITED STATES NATIONAL MUSEUM 



Very small specimens have short, broad, depressed rays. The permanent spines 

 make their appearance early, a specimen with R 9.5 mm. having about 12 in three 

 Beries on each ray, each surrounded by a circle of relatively large minor pedicellariae. 

 The big plates and spines are among the first to appear and their early differentiation 

 shows that the character is deep-seated. The smaller plates of the adult are second- 

 aries, the prominent plates being the first that are acquired by the young sea star. 

 There are about five series of single dorsal papulae, one intermarginal, and none 

 actinal; no actinal plates; adambulacral spinelets alternating one and two; tube feet 

 in two zigzag series or in four, arranged in quincunx. 



The young of acervata of the same general size (station 3232, 3233) have much 

 slenderer rays. An example of acervata with R 10.5 mm. has several of the radial 

 plates with two or three spines, the character showing itself early in this case, also. 

 The specimen with R 8.5 mm. shows the same tendency. 



In specimens of polythela with R 15 to 20 mm., the adult characters are readily 

 recognizable, although the actinal plates are wanting and the pedicellariae are still 

 relatively few. 



There is no evidence of an acervata stage in the development of polythela, nor 

 particularly, of the converse. 



Type— C&t. No. 15820, U.S.N. M. 



Type locality. — Arctic coast of Alaska, U. S. R. S. Corwin. 



Distribution.- — Bering Sea (Bristol Bay, vicinity of Unimak Island, Pribilofs, 

 St. Matthew Island, Petropavlovsk, Port Clarence) and the Arctic Ocean north of 

 Bering Strait, in from 2 to 59 fathoms, on gray, green, and black mud, or sandy mud, 

 exceptionally on coarse sand or gravel. Temperature range, 31.1° to 44.8° F. This 

 form appears to live on softer bottom and in colder water than does acervata. The 

 typical phase of the forma is found on mud or very fine sand, in water under 38°. 

 It is possible that the higher readings of 43° and 44° may be erroneous. 



Specimens examined. — One hundred and thirty. 



Specimens of Leptaslerias polaris acervata forma polythela examined 



Sta- 

 tion 



3236 

 3244 

 3245 

 32M 



3262 

 3253 

 32M 

 3255 

 3250 

 3277 

 3439 



3440 



3441 



Locality 



Bristol Bay, Ber.ng Bea 

 Mouth o( Bristol Bay _. 

 ....do 



North coast Unimak Island. 



.do.. 



.do. 

 .do., 

 .do. 

 .do.. 



North of end of Alaskan Peninsula 



West of Prlbilof Islands, 57° 06' N . 170" 



35' W. 

 West of Prlbilof Islands, 67° 05' N , 170" 



41' W. 

 West of Prlbilof Islands, 57° 04' 20" N., 



170° 52' 30" W. 



Depth 



Fathoms 

 14.75 

 4.5 

 11.5 

 25.5 



29.5 



36 



46 



43 



49 



IS 



41 



48 



Nature of bottom 



Bottom 

 temper- 

 atures 



Num- 

 ber of 

 speci- 

 mens 



Collection 



U.S.N.M. 



Do. 



Do. 

 U. S. N. M. (very 



large). 

 U.S.N.M. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 

 Do. 



