— 896 — 
versalem symmelrica. Phaeophora laminaeformia (quandoqiie granuli- 
formia), bina, medio zonas connectivales attingenlia. 
Conspectus generum 
!• — Frustala sine septis internis. 
A) Frustula solitaria, libere vigentia (Cfr. Vanheurckiam). 
* Valvae rhapheni haud sigmoideo-incurvani ostendentes (Cfr. Sco- 
liopleuram). 
Navicula Bory. — Valvae nodulo mediano rotundato donatae, trans- 
verse punctato-striatae vel haud medio interrupte costalae 
(incl. Pinnularia Ehr.). 
Stauroneis Ehr. — Valvae ut in Navicula, nodulo mediano trans- 
versim dilatato, staurum etTiciente, utroque fine haud bifido ; 
slriae haud decussatis. 
Pleurostavron Rabenh. — Est Stauroneis valvis in fasciam cohae- 
rentibus (Verisimillime Stauroneidis seclionem sistens). 
Sehizostauron Grun. — Valvae ut in Navicula sed nodulo mediano 
transversim dilatato hneari, utroque fine bifido. 
Stauroptera Ehr. — Valvae ut in Navicula sed costis medio spa- 
tio transversali levi interruptis (Vix, suadente ci. Brun, a gen. 
Stauroneide sejungendum). 
Staurogramma Rabenh. — • Est Stauroneis valvis striis decussatis 
inslructis. 
Vanheurckia Bréb. — Valvae ut in Navicula, nodulis et mediano 
et terminalibus inter duplicem rhaphem sitis (Fruslula tubo 
mucoso inclusa). 
** Valvae rhaphem arcuatam vel sigmoideam oslendentes. 
Staurosigma Grun. — Gharacteres Stauroneidis sed rhaphe sig- 
matoidea. 
Pleurosigma V^. Sm. — Valvae naviculaceae, plus m'nus sigmoi- 
deae, striis longitudinalibus, transversis et saepius simul obli- 
quis ornalae, nodulo mediano rotundato vel oblongo, rhaphe 
sigmatoidea. 
Scoliopleura Grun. — Valvae naviculaceae, valde convexae, tortae 
spiraliter et lune rhaphem et zonam connectivalem plus minus 
oblique sigmatoideas praebentes. 
Achnanthosigma Reinh. — Valvae Pleurosigmatls, frustula e zona 
connectivali visa arcuata, achnanthiformia (Vix a Rhoicosigmate 
sejungendum). 
