ASTEROIDEA 83 



carinated, paxilliform actinal plates, serial gonads. The lateral abactinal plates are 4- 

 lobed and regularly imbricated. The extreme lateral abactinal plates of L. magnificus are 

 also 4-lobed and imbricated, while the others are 5- or 6-lobed. Superambulacral plates 

 are present. In Mimastrella cognata there is an odd interradial series of actinal inter- 

 mediate plates extending from mouth plates a third of the distance to margin. If of no 

 great importance, this series is significant since it is found in most species of Lepty- 

 chaster. 



In diagnosing Mimastrella (loc. cit. 1916) I contrasted it with Radiaster (olim Mim- 

 aster), and stated that the tube feet have small sucking disks. They are not functional 

 sucking disks, but are mammiform, and narrower than the podium, as in Leptychaster , 

 and allied genera. 



No Leptychaster which I have examined has the 3- or 4-pronged terminally flaring 

 spinelets^ of Mimastrella. Whether this character, and the somewhat reduced, more 

 paxilliform, inferomarginals are of superspecific value, only other species oi Mimastrella 

 will demonstrate. 



M. cognata may be described as 2. Leptychaster With narrow inferomarginals, and highly 

 characteristic (mostly) 4-pronged spinelets. Whether such an aberrant species should be 

 given generic rank or relegated to a subgenus is a matter of opinion. Were it not for the 

 spinelets I would hardly hesitate to include it in Leptychaster. As matters stand it is 

 probably best to maintain a genus Mimastrella. 



Leptychaster kerguelenensis Smith 



Leptychaster kerguelenensis Smith, Ann. Mag. Nat. Hist., ser. 4, xvn, 1876, p. no. 



Leptotychaster kerguelenensis Smith, Philos. Trans. Roy. Soc, Zool. Kerguelen Island, CLXViii, 



p. 278, pi. 17, fig. 2.— Sladen, 1889, p. 184, pi. 31, figs, i, 2; pi. 32, figs, i, 2. 

 Leptotychaster kerguelensis , Koehler, 1917, p. 52, pi. 6, figs, i, 2, 7, 12. 



St. 1562. Vicinity of Marion Island, 46° 53' S, 37° 55' E, 97-104 m., 3 specimens. 



St. 1563. Vicinity of Marion Island, 46° 48-4' S, 37° 49-2' E, 101-106 m., i specimen. 



The specimen from St. 1563 measures R 53 mm., r 13 mm., br 15-16 mm. ; the largest 

 of the three from St. 1562 has R 23 mm., r 7 mm. 



Both Sladen (1889) and Koehler (1917) have described and figured this species. Their 

 largest specimens measured R 66 and 65 mm., r 13 mm. The specimen from St. 1563 

 agrees well with Koehler 's figures (1917, pi. 6, figs, i, 2). His fig. i shows the consider- 

 able disparity in size between the small paxillae of centre of disk and radial region of ray 

 and the obviously large ones of the lateral part of the abactinal area. Sladen's figure 

 does not bring this out. 



Koehler has also discussed Leptychaster antarcticus which Bell (1908, p. 9) recorded 

 as the young of kerguelenensis, although the type has a difi^erent oral armature and 

 more numerous adambulacral spines, differently disposed. Bell's large specimens of 



1 Koehler (1920) figures spinelets of accrescens, pi. 74, fig. i ; magnificus, fig. 2; fiexuosus, pi. 75, fig. 3; 

 arcticus, fig. 4 ; kerguelenensis, fig. 6. I have found that spinelets of anomalus, propinquus and pacificus are of 

 the general type of arcticus. 



