2 Proceedings of the Biological Society of Washington. 



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 Porcellanasteridse proper by 

 the presence of cribriform 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 between 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. 

 megaloplax has a conspicuous ' ' anal ' ' aperture. This difference 

 between Prionaster and Ctenodiscus must be weighed against the 

 important common characters mentioned above, I would sug- 

 gest that the genera be rearranged as follows : 



Family Qoniopectinids. 



Characters. — Specialized fascioles or cribriform organs between all the 

 marginal plates; actinal plates in double transverse series, there being 

 between every pair a specialized fasciolar channel, roofed by webbed 

 spinelets, leading from the marginal fascioles to the furrow ; ampullae 

 single; superambulacral plates present ; abactinal skeleton astropectinoid. 



Subfamily Ctenodiscinse. 



Characters. — Marginal cribriform organs consisting of superimposed 

 transverse webbed combs of spinlets; intestinal ccecum obsolete ; no in- 

 testine. 



Included Genera. — Ctenodiscus Miiller and Troschel; ? Pectinidiscus 

 Ludwig.* 



Subfamily Goniopectininse. 



Characters. — Marginal cribriform organs consisting of discrete spinelets 

 covered by a single webbed series on the transverse margin of the plate ; 

 well developed intestinal coecum, intestine, and apical pore. 



Included Genera. — Goniopecten Perrier and Prionaster Verrill. 



Craspidaster. — Craspidaster hesperus (Miiller and Troschel), 

 which resembles the Goniopectinidse in having a single series 

 of webbed peripheral spinelets on the marginal and actinal 

 plates, differs in lacking the characteristic double serial arrange- 



* Pectinidiscus has not as yet been fully described. 



