232 



CONllUBUTIONS FROM THE NATIOI^AL IIERBArJUM. 



b. Valve rinular, divided into complete or incomplete sectors by radiating 



ridgeti or wide hyaline liml>s; no horns ov pronunc^nt spnies, (Actino- 



DISCEAE,) 



a. Valve partly or fully divided into sectors by radiating ridges ninniiig 

 from the margin toward or to the center; marldng strong; margin 

 massively sculptnred; no process at the marginal end of the 

 dividing ridges; sectors ail on one plane. (Stictodiscixae.) 



Valve smface flat or nearly so; ra<lial ridges many, the main 

 ones reaching the gt^neraliy rosotted center; more or less 

 tmiled to each other by concentric cross linesj thereby giving 

 a spider-web sculpturing to the valv(S nutline of valve 



uniformly circular IIcmiptyeMis (p, 26r>). 



Valve surface often elevated at the center, one vah'c of the frus- 

 tule more so than the other; radial ridg(\s generally lew, rarely 

 reaching the center, which is without a rosette; no deiiinte 

 concentric lines forming a spider-wt^b )>attern, thougli a shad- 

 owy reticulation is sometimes pn^sent. Outline of valve 



w 



sometinu's polygonal Stidodiscus (p. 267). 



b. Valve divided into sh:n*ply distinct sectors by radial ridges uni- 



formly running from the margin ia tlu^ hyaline central area; small 

 but evident spines usually at the marginal ends of these dividing 

 ridges; alternate sectors generally depressed; that is, sectttrs in 

 two planes (Actinoptvcuixae) Adinopiychus (\). 2(59). 



c. Valve sharply divided in(o sectors by broad liyaiine bars or limbs 



running from a hyalin<' center toward or to the margin, tln^ir outer 

 ends marked with a minute wart or spine; the liyaliiu,^ center 

 divided into m(m? or less wedge-shaped divisions ctmflueni ^villi 

 the limbs; spaces between the radiating li!nl)s marked with iinc 

 but closely set beading, arranged in radial or dcKHissating order, 



(ASTEROLAMPRIN A E . ) 



Radiating limbs all of the same widlli and generally (apeiing (o 

 the margin; central area either retirulated or divided by 



straigliL linens into the same nundjerol parts as ilie limbs. 



Aslerolantpra (p. 272), 



One of the radiating ]ind)s narrower llian tlu^ofhers; limbs not 



tapering to the margin; central area tu^ver reticulated; uiu^- 



qtially divid<Hl into the same nund)er of part?^ as the limbs ])y 



zigzag lines Askromphahis (p. 273). 



c. Valve circular; surface impcM'fectly divided into s(><'tors l^y alternate undu 



laling elevations and dc^pressions, which [^re higlu^st and lowc^st at the 

 margin and decrease or di^^appear toward the center; each elevation 

 ]>earingat its highest point a blunt nippledike horn, pointing ra<lially 

 outward and upward. (TiartM)iscEAE) Tnpodiscus ('p. 277). 



d. Valve circular or round (dliptical; surface maiked Avith two (rarely nion 



only one) large opposite submarginal ocellae or ringed eyes, slightly or 

 considerably elevated above the plane oi tlu' valve; valve niarkings of 

 beading, lines, or both, arranged symmetrically with reffTcnce to the 



ocellae. ^Aulisceae) inlisms (p. 281). 



B, Valve oval or circular; frustule long-cylindrical, the 7onal diameter mucli ex- 

 ceeding the valval; zone mad(^ up of a series of rings or imbricated bands, 

 without internal septa; frustules unihHl into chains by their valves, (Solen- 



OIDEAE.) 



Valve in tlie form of a tall, tapering cone, its apex exccMitrically placed 

 and tipped with a stout, sometimes very long, hollow l>ristle or spin(\ 



Rhizosolenia (p. 283). 



or 



