MOIRA ATROPOS. 365 



MOIRA. 



Moira A. Agass. 1872. Rev. Ech. Pt. I. 



Test moderately thin, ovoid ; ambulacral petals sunken ; test bulging towards 

 interior in five pouches from five narrow deep grooves, like radiating spokes 

 from the abactinal pole, edged by the peripetalous fasciole which forms round 

 them a smooth border. Lateral fasciole passing at a considerable distance 

 under the anal system, as in Agassizia and Schizaster ; tubercles arranged 

 upon the upper surface diagonally. Actinal plastron elongated, pentagonal, 

 covered by larger tubercles, with ill-defined scrobicular circle carrying spathi- 

 form spines; only two posterior genital openings. Anterior groove extending 

 to actinostome. 



Gray has subdivided Schizaster into three genera, following the three 

 types of the Catalogue Raisonne ; he has, however, retained for S. 

 atropos the name of Schizaster, and separated the closely allied species S. 

 canaliferus and S. gibberulus, placing them respectively in the genera 

 Brisaster and Nina. The subdivisions of Michelin made at the same time, 

 more in accordance with the affinities of the species, are retained here. To 

 distinguish this genus from the same generic name previously used by Leach 

 and Huebner, I have changed the name to Moira: — 



Moira atropos 



! Spatangus atropos Lamk. 1816. An. s. V. 



! Moira atropos A. Agass. 1872. Rev. Ech. Pt. I. 



PL XXIII. 



Outline from above elliptical (PL XXIII. f. 1, 5) ; when denuded of 

 spines, slightly angular near junction of interambulacral plates. The plates 

 of test are all somewhat conical (PL XIII. f. 6), resembling shield plates of 

 turtles rising slightly towards one side and tapering towards the edge ; 

 from their highest point the tubercles radiate irregularly towards the edge. 

 The angular outline increases greatly with age, and in older specimens this fea- 

 ture becomes quite prominent, while in younger specimens the tendency is to be 

 more and more ovoid. Part of the posterior edge of the apical part of the 

 anterior ambulacra projects over the anterior edge, completely closing the 

 upper portion of the anterior lateral ambulacra (PL XXIII. f. 5). It then re- 

 cedes again, and the ambulacral groove thus appears to commence at a dis- 

 tance from the apex and make a marked angle with the longitudinal axis. 



