44 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



actinal plates with the intervening fasciolar channels, the similar 

 structure of the marginals, between which are cribriform organs, 

 and the similar form and aiinature of the adambulacral and mouth 

 plates. 



All species of Goniopecten and Prionaster^ however, have single 

 ampullae, thus eliminating the principal supposed difference between 

 these genera and Ctenodiscus. What I formerly regarded as the 

 lower lobe of the ampulla in Prionaster proves to be only a swelling 

 probably due to the extreme contraction of the muscular vesicles. If 

 the swelling has any significance at all, it is the merest rudiment of 

 a ventral lobe and the ampullae are to be regarded as single. This 

 fact seems to make it advisable to unite the three genera in a single 

 family which would be separated from the Porcellanasteridae proper 

 by the presence of cribiform organs between all the marginals,^ by 

 the actinal fascioles, and by the presence of superambulacral plates. 

 Although an apical pore may be present in Ctenodiscus^ I have also 

 dissected specimens in which I could find no trace of an opening, 

 nor of a tubular connection betM-een the stomach and the " epiproctal 

 cone." In the middle of the dorsal side of the stomach there is 

 a roundish lobe of small size which may represent the degenerated 

 rudiment of a coecum. Prionaster elegans^ on the other hand, has 

 a fairly large, butterfly-shaped coecum, connected with the apical 

 pore by a definite tubule. P. megalo'plax has a conspicuous " anal " 

 aperture. This difference between Prionaster and Ctenodiscus must 

 be weighted against the important common characters mentioned 

 above, and stated in the diagnosis of the family. On account of its 

 more Porcellanasterid characters Ctenodiscus may well come first 

 in the family. Presumably Pcctinidiscus belongs here also, parallel- 

 ing the characters of Prionaster. 



Subfamily Ctenodiscinae Sladen. 



Diagnosis. — ^Marginal cribriform organs consisting of superim- 

 posed transverse webbed combs of spinelets: intestinal coecum obso- 

 lete ; no intestine. 



Genus CTENODISCUS Muller and Troschel. 



Ctenodiscus Muller and Troschel, 1842, p. 76. Type, Asterias crispata 

 Retzius. 



CTENODISCUS ORIENTALIS Fisher. 



Plate 2, figs. 2-4 ; plate 7, figs. 1, la-e. 



Ctenodiscus orientalis Fisher, 1913a, p. 601. 



Diagnosis. — Differs from Ctenodiscus crispatus in having longer 

 and relatively much slenderer rays, on which the paxillar area is 



* An exception in Denthogenia. 



