230 CONTRIBUTIONS FKOM THE NATIONAT, HERBARIUM. 



ANNOTATED CATALOGUE OF GENERA AND SPECIES. 



The following key to the genera included in this report is offered 

 merely as an aid in identifying these genera. From a phylo<^enetic 

 standponit its value is probably small. The arrangement is practi- 

 cally that of F. Schutt in Engler & Prantl's Pflanzenfamilien - the 

 changes bemg mainly the restoration of the earlier names of some of 

 the genera m the place of those given by Schutt. Some sli-dit rear- 

 rangement has been found necessary, for reasons explained in the 

 text, as the placing of VnnlKuirckia, Reicheltia, and other genera 

 under l^nistuha, and the closer unioji of Actinocychis with Coscino- 

 discus. ]\Ii,u)r changes in the wording were also required in a few 

 places This general arrangement of Schutt appears more workable 

 than that of II U Smith/> on which it is partly based. Thev both 

 avoid the fatal difficulty of tlie classification of Pfitzer,^ worked out 

 on the basis of chromatophores, etc., of the living cell Althou-h 

 rtitzers arrangement is of great biological value, its distinctions a're 

 so uncertain of apphcation to the diatoms as a class, the great maioritv 

 of which are known only in a fossil state, tluit it can never come into 



mic 



No attempt is made here to carry the classification down into the 

 seimrate species of the different genera. Despite the great industry 

 and ability in making keys to the species based on verbal distinctions 

 exhibited in the monographs of Cleve, Kattray, and other diatomists, 

 tiie writer must confess to his inability to use these with anv feelinc. of 

 security. Verbal descriptions are very valuable, but withmit accom- 

 panying dlustrations they are rarely conclusive. The differences 

 between spcx:ies being based on tlie varied and nften immenselv coni- 

 phcated sculpturing of the valves, it is almost impossible to d'escribe 

 these (hflercnces clearly and at the same time tersely enough to serve 

 the purpose of analysis. A good photograph or drawing of a diatom 

 will always_ be of more value for identification tlian any amount of 

 word painting. As it is not practicable to accompany (lus report 

 with figures of all the species here enumerated, copious references are 

 given to works m wliich satisfactory illustrations are to be found 



SYNorxnAr kky. 



Subfan.ly I CENTEICAE. Valve centrally built; .lua i., ur,-a„ged in relation to 

 a central point or focu« rather than in relati<,n (o a nu.lian line; outline eircnlar 

 oval or ell.ptieal, sometimes polygunal, rarely cre^vnt-shaped or spindle-shaped' 

 neither a raphe, eryptoraphe, nor pseudoraphe present; vahe-niarkings either 

 concentne radial, decussating, or irregular, never pinnate; processed (horns, 



Hpuu\^, oU'.) common. 



"Pflanzenfamilien, A. Engler & K. Prantl, Theil I, Abteilung ]G. Leipzi. 1896 



^Conspectus Dia.omaceae, ILL. Smith, The Lens 1 : 1-J9, 72-93 lo4-157^^S- 

 <=Hanst. 13ot. Abhand, 3: 187L JO^ia.. J.S,.. 



