Classification 123 



and stellate or stellate-sinuate ; girdle generally complex, with numerous inter- 

 calary bands which are sometimes scale-like. Includes Biddulphiese, Tabellariese, 

 Licmophorese, and Entopylese. 



C. Valves usually linear or lanceolate ; girdle simple ; generally with a pseudoraphe 

 in each valve. Includes the Diatomese, Fragilariese, Synedreae, Raphoneidese, 

 and Plagiogrammeae. 



II. Mobiles. Diatoms which exhibit spontaneous movements. Conjugation known 

 in all the families. 



A. Raphe imperfect or keeled (carinate). Includes Eunotieaj, Epithemieoe, Nitz- 

 schieae and Surirelleae. 



B. Raphe perfectly formed, and interrupted in the middle of the valve, which is 

 also furnished with central and terminal nodules ; more or less extensive central 

 and lateral areas occur in relation to the raphe. Includes the Heteroideae, 

 Tropidoidese, and Naviculoideae. 



Forti has given the details of the genera of the section ' Immobiles ' 

 and of division A of the ' Mobiles.' Division B of the latter section, which 

 includes all the naviculoid diatoms, was very carefully and comparatively 

 synopsized by Cleve in 1894-5. 



It seems very desirable to combine the most important features of both 

 the above classifications. Schiitt's divisions of the Centricse and Pennatae 

 are so fundamental, probably representing two distinct lines of descent, that 

 they cannot be discarded. Also, in view of the fact that all the centric 

 diatoms are non-motile, it might be much wiser to restrict the differentiation 

 between the motile and non-motile forms entirely to the Pennatae. This 

 differentiation would then quite coincide with the degree of development 

 of the raphe, which is without doubt the most important morphological 

 structure of the pennate diatom. 



The author would therefore suggest the following classification of diatoms : 

 Class BAGILLARIE^. 

 Order I. CENTRKLE. 



[Includes divisions A and B of the ' Immobiles' of Forti.] 

 Order II. PENNATAE. 



Sub-order 1. Non-labiles. 



[Includes division C of the ' Immobiles ' of Forti.] 

 Sub- order 2. Labiles. 



[Synonymous with the ' Mobiles ' of Forti.] 



A. Raphe imperfect or keeled. 



B. Raphe perfectly formed. 



