MELOSIRE/F. 



429 



Tribe XX. Mflosiref.. 



Frustules apiculate (the 



extremities of the margin 



drawn out into a point), 



not radiate. 



{ Frustules f Frustules showing in the girdle face a simple 



I cylindrical, [ or alate apiculus . . Pyxilla. 



with \ 

 j dissimilar | Frustules showing in the girdle face a comb 

 \ valves. [_ of alate spines welded at the base . Ktenodiscus. 



I Frustules not cylindrical, apiculate in the valve face ; valves 



L similar ...... Peponia. 



f One or more spines, central, coronal or scattered, robust, 

 rather short ; but no internal costns . 



Stephanopyxis. 



Frustules cohering 

 by the spines. 



1 Numerous scattered spines, sometimes also round the valve ; 

 valve with broad margins, furnished with internal costas 

 on the girdle face ..... Muelleriella. 



Valves furnished with narrow and very long marginal spines ; 

 spines simple or branches all of equal length . . Skeletonema. 



v 



> 

 o 



X! 



o 



Frustules cylindrical, with somewhat large regular marginal teeth and a 



peculiar central clasping spine 



. Syndetocystis. 



, r , ... , f Valves furnished with a peculiar hooked central 



Valve elliptic or sub- du , . Rutilaria, 



linear, with spines or 1 *!.. 



marginal teeth, and the \ Valves linear, with median portion inflated, elliptic, 

 "fl t h" ? 1H without any peculiar nodule; linear portion 



inflated elevated. ^ smoo th, with spines, without septa . . Clavularia. 



I I 



f Frustules cylindrical ; ends first constricted and finally expanded into a 

 connecting nodule ..... 



Frustules united by a delicate mucous thread ; valves 

 slightly silicious, having small marginal spines and 



o 



Strangulonema. 



Frustules 



united 



into long 



filaments. 



radiating dichotomous striation 



Thalassiosira. 



j Frustules closely united, ro- ( Frustules and valves 



bust ; valves circular, very j with cellular structure . Endyctia. 



silicious, often furnished with -! 



small teeth at the junction | Frustules and valves 



of the frustules. { punctate, not cellular . Melosira. 



f Valves somewhat hyaline and conical or inflated in girdle 

 view, showing costag or ribbed lines in girdle view ; 

 apices often truncate or spinous ; interspaces punctate . Mastogonia 



Frustules 



united by 



twos and 



threes. 



Valves apparently hyaline and showing from 3 to 5 



mammiform elevations 



Frustules compressed, subquadrangular 

 elliptic .... 



Pantocksekia. 



> 

 o 



c3 

 > 



valve 



Druridgea. 



f Valves with areolate margin and hyaline, 

 umbilicate centre . 



Valves 

 round, 

 convex, 

 like a 

 watch- 

 glass. 



Margin 



not 

 arcoate. 



I I 



Centroporus. 



' Valves regularly striate- 

 punctate throughout the 

 surface . , Podosira. 



Valves with umbilicate cen- 

 tre, very finely striate, 

 sub-hyaline . , Hyalc-discus. 



