122 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



interrndius, however). The abactintil plaies arc structurally like those of Luidiaster 

 and Clieiraster rather than of Benthopeden, to which the presence of odd inter- 

 radials would naturally ally the genus. The dorsal muscle bands are very weak 

 in Nearchasier and well developed in Myonotus, and are nearer to Benthopeden 

 than to Luidiaster in the mode of attachment of the proximal ends. The very 

 spiny marginal jilatcs suggest Luidiaster rather than Benthopeden. Even Ben- 

 thopeden may lack some of the odd interradial marginal plates as regularly occurs 

 in B. mutabilis. In other words, Nearchaster stands nearly halfway between the 

 two groups, and furnishes convincing evidence of the close relationship of Bentho- 

 peden on the one liand and Cheiraster and aUies on the other. I have not main- 

 tained the two families so ably expounded by Ludwig, because I do not think a 

 sharp line of separation can be drawn. 



Whether the Benthopectinidai should be regarded as a distinct order, the 

 Notomyota, is wholly a matter of ojnnion. There are unfortunately no rules to 

 determine what shall constitute ordinal characters. The Porcellanasteridae are 

 probably just as deserving of ordinal rank since they possess a set of special char- 

 actei-s winch set them apart from the other Phanerozonia. The fact that the 

 Notom^'ota is not here adopted simply means that the writer has preferred to use 

 characters of wider apphcation. It may well be that the solution of the present 

 unsatisfactory condition of the orders of Asteroidea will be the recognition of 

 numerous smaller groups; about four in the Phanerozonia and two in the Spinulosa. 



I have followed in the main Ludwig's arrangement of genera and species. I 

 am not at all sure of the validity of Marcelaster. I have not adopted Pararchaster, 

 since it is separated from Benthopecten by a rather trivial character, or at least by a 

 variable and difficult one. 



For a systematic and historical account of the genera and species of the Noto- 

 myota, Ludwig's paper should be consulted. Two new genera (with four new 

 species) have been added to Ids list, one new form to Pedinaster, and two to 

 Benthopeden. 



Genus PECTINASTER Perrier. 



Pectinastcr Perrier, Ann. sci. nat., vol. 19, 188.5, art. 8, p. 70. Type, P.filholi Perrier. Exped. 



sci. du TramilleuT et du Talisman, 1894, p. 278. — Ludwig, Sitzungsber. k. preuss. Akad. 



Wisi!., vol. 23, 1910, p. 448. 

 Pori(a«<fr Sladen (part). C/mZ/cni/CT- Asteroidea, 1889, p. 23. 

 Cheiraster Ludwig (part), Asteroidea, 1905, p. 1.— Fisher, ZooL Anz., vol. 35, 1910, p. 551. 



Diagnosis. — Benthopectinidse lacking odd interradial marginal.^, with the 

 abactinal plates a very simple form of low paxilltB, bearing numerous spinelets 

 and with entire (not two-lobed) more or less swollen papularia; pedicellariae when 

 present fasciculate, confined to a single plate, or standing on two adjacent plates, 

 occiirring on actiual intermediate plates, or also on the marginals and abactinal 

 paxilliB; marginal plates small, usually elongately oval or subtriangular in form, the 

 two series having a tendency to alternate more or less, causing the horizontal 

 margin that touches the companion series of plates to be more or less definitely 

 aiigulated or to form two facets; actinal interradial areas with very few interme- 

 diate plates; these small and without order. Armature of adambulacral plat«s 

 (1) a semicircular furrow series of small spines, and (2) one, usually larger and 



