18 BULLETIN 76. UNITED STATES NATIONAL MUSEUM. 



rfi. One or two conspicuous recurved hyaline teeth to each pair of mouth plates; an odd inter- 

 radial marpinal Odontaslerida; p. 153. 



(f. No conspicuous recurved hyaline teeth; odd interradial marginal present in one genus. 

 «'. Spinelets of tabulate paxilliform plat«s very slender and glassy; marginal plates small, 

 not much larger than adjacent actinal plates; odd marginal present; actinal interradial 

 areas small; tabulate abactinal plates with internal radiating ossicles; calcareous inter- 



bracbial septa; ampullae single Chsetasteridsefi 



e'. Spinelets not slender and glassy; no odd interradial marginal; abactinal plates tabulate or 

 paxilliform; ampullae double. 

 /■'. Abactinal plates tabulate, paxilliform, arranged in oblique transverse rows on either side 

 of a conspicuous medioradial series and with special internal imbricating ridges; actina! 

 intermediate plates aborted or very few; interbrachial septa calcareous; gonads extend- 

 ing far along rays; general facies astropectinoid Archasteridse.b 



p. Abactinal plates tabulate, often paxilliform, not arranged in definite oblique series; no 

 internal imbricating ridges; actinal interradial areas large, with numerous plates; inter- 

 brachial septa usually membranous; gonads interradial Goniasleridve, p. 158. 



6*. Abactinal plates are neither tabulate nor paxilliform, but are flat, convex, spinous, tubercular, 

 granulous, or smooth; are sometimes overlaid by a thin or thick, smooth or granulous, skin; 

 marginal plates with or without robust spines or tubercles, 

 c'. Disk large; actinal interradial areas extensive, but no papulae on actinal surface. 

 <f'. Marginal plates large, conspicuous; abactinal skeleton composed of polygonal, circular, or 

 stellate plates united into a firm pavement; with or without secondary abactinal inter- 

 mediate plates; plates may be smooth, granulous, spiny, tubercular, or covered by a smooth 

 or granulous skin; papulae single, or a few to an area, not numerous and in circumscribed 



are.is; interbrachial septa usually membranous Goniasteridx, p. 158. 



rf". Marginal plates large but as a rule inconspicuous, being more or less hidden by granulous 

 skin or encroachments of papular areas; abactinal skeleton stellato-reticulate; plates always 

 granulous; papulae numerous, and in definite areas; abactinal plates usually with large 

 conical tubercles or spines. Disk usually high, or body thick and cushion-like ; interbrachial 



septa usually calcareous Oreasteridx. 



(f. Marginal plates small, more or less imbricated and whole body covered by thick, smooth, 

 tough skin; abactinal skeleton tessellate or reticulate, the plates loosely imbricated; prom- 

 inent spines exceptional, small spines present in some genera Asteropidif, p. 247. 



c'. Disk small, with verv small actinal interradial areas as a rule (if at all well developed, then 

 papuhc on actinal surface); marginals small; skeleton tessellate; tegumentary developments 

 granulate (skeleton overlaid by a smooth skin, without prominent spines in Leiaster) 



LincHidic, p. 240. 



CHARACTERS USED IN THE CLASSIFICATION OF PHANEROZONIA. 



In <li\-i(ling an order into families, one endeavors to use ordy those characters 



which are of more tlian generic value yet which are not wide enough in scope to be 



of use in suhdividing the class, that is, are not of ordinal importance. In determining 



the order I'hanerozonia the ambital skeleton and distribution of the respiratory 



o The classification of Chxiasler presents unusual difficulties owing to the intermediate nature of 

 the genus. It does not appear to belong in the Linckiidae, nor in any other family. Ludwig created 

 the Chsetasteridae as a provisional gro\ip. The presence of an odd interradial marginal, and in one spe- 

 cies of rudimentary recurved teeth suggests Odontasler, but unlike that genua and its allies, the inter- 

 brachial septa of Chxlaster are calcified, and the ampullae single. In some respects the genus shows a 

 remote alliance with the Ganeriidse. 



(>The old and well-known genus Archaster is an isolated and remarkable tvpe, for, though superfi- 

 cially re.«embling Astropeclen, it is really near the Goniasteridse. It has heavily calcified interbrachial 

 septa, no superambulacral ossicles, tabulate abactinal plates, those of the regular oblique transverse 

 series imbricating by curious internal keels, produced toward the midradial line. The very regular 

 and enlarged radial series of plates and the readily recognizable primary apical plates recall the Goni- 

 a.ir>n<l;r. Tho ampulla; are strongly double, and the tube feet have hea\'>^ sucking disks. 



