16 Acta Societatis pro Fauna et Flora fennica, Till. n. 2. 



small group of Nav. palpebralis, which has no longitudinal lines, 

 is perhaps to be placed in the vicinity of the formosae. A real 

 affinity with the forms of the formosae group is shown by 

 the quadriseriatae-group (Grun. in Arct. Diat. p. 29) as Nav. 

 aemula, N. consimilis, N. subdivisa, N. latefasciata, N. blanda, N. 

 Powellii. Other, included in this group, as Nav. Bruchii and Nav. 

 superimposita, belong to the radiosae. Stauroneis robusta Petit 

 belong to Trachyneis. 



The group of Nav. didyma comprises a large number of clo- 

 sely connected forms and is so well defined that it may be most 

 conveniantly treated as a separate genus, for which the old name 

 Diploneis, given already by Ehrenberg, may be reserved. In this 

 genus the nonconstricted forms (N. Smithii, N. elliptica, etc) may 

 also be included, as they agree with the didyma? in all respects 

 except the form of the valve, which is of no real importance. 



Although there are reasons for splitting up the Naviculae of 

 the groups radiosae, punctatae, and formosae into three genera, I 

 am not for the present inclined to do so in this paper, but on 

 the other hand I admit the genera Pinnularia, Neidium, Anomce- 

 oneis, Frustulia and Diploneis. 



Several of the smaller groups of Navicula are not natural, 

 as pseudo-pleurosigma and minutulce. The former is founded on 

 the opposite directions of the end-fissures of the raphe, and com- 

 prises forms, belonging to Pinnularia (Nav. Flamma, Nav. platy- 

 cephala) and to the group formosae (Nav. anomala). Several forms 

 of punctata? have the endfissures in opposite directions. The mi- 

 nutulae comprise generally small species, which often have very 

 little connection with eachother. 



The genus Scoliopleura, formed for species with sigmoid 

 raphe, is not natural, sigmoid forms being met with in widely 

 different groups. Thus Nav. Raeana Gastr. comes nearest to Nav. 

 yarrensis, which may be either a Pinnularia or a form of the 

 group radiosae. A species of Scoliopleura, from the Mediterranean, 

 not yet described, comes nearest to Nav. superimposita. Scolio- 

 pleura tumida is widely different from Sc. convexa and Sc. Peiso- 

 nis, which may perhaps be classed together with N. Schneideri 

 from the Caspian Sea. 



The genus Elwiconeis comprises the species R. Garkeana 



