20 BULLETIN 16, UNITED STATES NATIONAL MUSEUM. 



ficatory purposes. This may be true, but paxilhT, wl.icli leave arcade-like spaces 

 for the circulation of water about the papuliv, are just as directly related to the 

 same habit, as also are the various sorts of fasciolar channels between the marginal 

 and actinal intermediate plates, and the still more specialized cribriform organs 

 i.f the Porcellanasteridff. Unless climbing, a starfish does not move by attaching 

 its suckers to the bottom and drawing itself along, as is sometimes stated, but 

 it rests on the tips of the tube feet," which are manipulated like a centipede's legs. 

 Consequently a starfish with suckers can walk or crawl on muddy bottom, and 

 those with pointed lube feel can crawl on hanl bottom, as they do. For example, 

 Leptychaster, Perse phonastcr (PsilaMeropsis), Astropecten, Cterioph or aster, Patagiaster, 

 Luuiia, Ctenodiscus, and some other genera with pointed tube feet frequently 

 occur on hard sandy bottom, on gravel, on sand, coralline, and shells, or on mixed 

 coral and coral sand and shells. Similarly, members of the following families 

 with suckers on the tube feet live on soft mud, and, for aught we know, have for 

 ages. If the tube feet changed readily it is curious we do not find some of these 

 families having genera with pointed tube feet. Benthopectinidie, Chretasterida!, 

 Odonf asterid<T?, Archastcridse Goniasteridie (all subfamilies) , Oreasteridse, Asteropida^, 

 Linckiidie, and practically every family of the Spinulosa and Forcipulata (Crypto- 

 zonia). There are more species, with suckers, living on globigerina ooze than there 

 are with pointed tube feet (for comparison see Sladen, 1889, p. 713). T think it is 

 evident that the pointed tube feet constitute a conservative and deep-seated 

 character. 



Since the pointed tube feet are of superfamily importance, it follows that 

 Sladen's Archasteridae, still used by most writers, is an unnatural group, as it 

 contains both types of structure. The family can not be diagnosed in a rational 

 manner. When the heterogeneous elements composing it are partitioned in other 

 groups where they belong, nothing is left but the genus Archaster, which is an 

 aberrant type of uncertain relationships. As Yerrill has already indicated, the 

 family should be retained for this genus only. 



Tiie reasons for enlarging the AstropectinidiP are discussed under that family. 



The families having well-developed sucking disks to the tube feet are as follows: 

 Benthopectinidje (PararchasterLn.T of the Archasteridse Sladen), Archasteridffi 

 (restricted), Odontasteridae (part of Pentagonasteridse Sladen, and Archasteridse 

 Perrier), ChoetasteridEe (part of Linckiiihi^, most authors except Ludwig), Goni- 

 asteridse (including Antheneidie), Oreasteridie, Asteropidae, and Linckiidse. The 

 Benthopectinidae are readilj' separated on account of their more or less alternate 

 very spiny marginals, dorsal muscle bands, long slender rays, restricted papular 

 areas, rudimentary paxillae, and the characteristic form of the pedicellariae when 

 present. They possess a combination of characters not duplicated even in part in 

 any other family. Ludwig has recently raised this group to ordinal rank (Noto- 

 myota). The Odontasteridae, Chtctasteridse, and Archasteridae are small families. 

 The first and perhaps also the last are related to the Goniasteridae. The Chsetas- 

 teridaj are extremely puzzling. I have placed them in the key next to the Odon- 

 tasteridae, but the group is difficult to classify. The gla-ssyspinelets are duplicated 

 elsewhere only in the Spinulosa, but the structure of the abactinal tabulate plates, 



a See Jennings; Behavior of Asterias forreri. 



