Frustula e facie valvari visa plerumque bacillaria, subinde late 

 ovata, seraper (saltem in una alterave valva) rhaphe genuina distincta 

 nodulisque et centrali (rarissime nullo vel obsoleto) et terminalibus 

 instructa, dentibus, spinis, aculeis vel processibus carentia. 



Conspectus Familiarum 



I. Valvse similes h. e. utraque rhaphem nodulurnque centralem 

 genuinum praebens. 



A) Frustula e latere connectivali visa secus axin transversalem symmetrica 

 (rarissime asymmetrica) *), rhapbe recta vel incurva. 



* Latus valvare secus rhaphem rectam vel incurvam (axin iongitudinalem) 

 symmetricum. 



Naciculacece. Valvse turn explanatae haud carinatae, tum utrinque 

 prope raarginem carina praeditae, carina media nulla **). 



Amphitropidacece. Valvie alte convexae, carina mediana et cari- 

 nis duabus lateralibus instructae. 



** Latus valvare secus axin longitudinalem asymmetricum. 



Cymbellacece. Rhaphe uno margini approximata vel arcuata. 



B) Frustula e latere connectivali visa secus axin transversalem asymmetrica. 



Gotnphonemacece. Frustula clavata. 



II. Valvae dissimiles h. e. uua tantum rhaphem nodulumque cen- 

 tralem genuinum prabens. 



Cocconeidacece. Valvae rotundatae seu elliptica?, superior pseudo- 

 rhaphem, inferior rhaphem genuinam nodulumque centralem plus mi- 

 nus evidentern ostendens [Frustula arcuato-geniculata ita ut rhaphe 

 culraen sistat]. 



Achnanthacece. Valvse oblongse, superior pseudorhaphem, inferior 

 rhaphem genuinam nodulumque centralem ostendens (Frustula ita 

 arcuata ut axis transversalis culmen sistat]. 



*) Ci'r. genera Rhoiconeidem, Rhoicosigma etc. ia-Naviculaceis. 



**) In Naviculaceis genus insigne Amphipleuram Kuetz. tum ad Surirella- 

 ceas, tum ad familiam propiiam ( A mphipleuraceas) vel ad Naviculaceas re- 

 latum, praeeuntibus Van Heurck, Truan etc, inclusi. Adest revera magna re- 

 latio inter hoc genus et genus Frustuliam (Ag.) Grun. cui species omnes 

 Vanheurchice duxi. 



