<'<)\S|'K(Trs OF TIM-: FAMILIES AND GKNERA. 



23 



Frustules cohering; quadrangular in f. v.. valves 

 without central nodule; striae interrupted by a 

 smooth median line or a blank space; \al\es in 

 fluted or constricted; terminal nodules present. 



and generally prominent in f. v DLMKKKI; UAM.M A \\\. 



I Frustules not as above s 



I Frustules with a serrated snl ure : valves without a 

 s median line, and with transverse conspicuous rows 



of pores or dots. .. Tcrebn/ria \ x v r. 



Frustules not as above . . ) 



Frustules in f. v. narrow, linear; valves lanceolate 

 or inflated; with conspicuous moniliform (gener- 

 } .j ) ally somewhat radiate), transverse striae; and a 

 median line or black space (frequently obscure or 



wanting); nodules absent RAPH<>\I;IS xxvu. 



I Frustules not as above 10 



i Frustules sessile, solitary, or in twos, elongated. 

 linear; slightly cuneate ; valve finely striate. con- 



10. i stricted at one end. and without median line 



Peroiiitt \\vni. 



I Frnst ules not as above 11 



| Frustules linear in f. v. ; somewhat hyaline, and en- 

 larged at one end ; valves striate, without median 

 . line or nodule ; cuneate, and constricted at one 

 end ; united in a stellate or zigzag manner 



A.STERIONELI.A XXIX. 



L Frustules not as above IL* 



Frustules much elongated; valves with a smooth 

 median line or blank space, sometimes obscure : 

 frequently a central pseudo-nodule; transversely 

 '- I striate, never costate ; sometimes slightly cuneate, 

 or bent, sessile, filamentous, or attached end to 



end SVNKDRA x\\. 



v Frustules not as above 1 : ! 



I Frustules very much elongated, straight or undulate; 

 valves inflated at the middle, slender < awn-like . 

 1.'!. somewhat irregularly punctate in s. v., without 



median line, or nodules To.fftritnn xxxi. 



Frustules not as above 1-4- 



f Frustules cuneate ; margin smooth; valves hyaline. 

 I - or finely striate, with a median line 



LH'IUnl'lloUA \\XMI. 



' Frustules not as above . Hi 



