KONGL. SV. VET. AKADEMIEX8 HANDLIXGAR. 



BAND 26. X:0 2. 



179 



a unilateral row of stigmas. Grdnow has formed for the species with stigmas the group Asym- 

 metrica, and for those without stigmas the group Symmetrica, which names may in view of 

 maintaining the analogy with the Cymbellfe be adventageously changed to Stigmatica and Astig- 

 matica. 



There is a great resemblance between the cell-contents of Gomphonema and Cymbella, the 

 structure is the same in both genera, and they are no doubt nearly connected. We have in Cym. 

 Beccarii Grun. a form, which is asymmetrical to the transverse axis, and, there are several other 

 Cymbelloid varieties of Gomphonema. Goinph. Cymbella Brun may be considered as an inter- 

 mediate link between the two genera. 



The outline of the forms of Gomphonema is very variable, and older authors have paid too 

 much attention to it in forming new species. There exist in the same species all possible transi- 

 tions, from purely clavate, to strongly biconstricted forms, so that outline only cannot be regarded 

 as a good specific distinction. 



Most species of Gomphonema inhabit fresh water, some brackish water, and there are also 

 purely marine forms, the latter being all astigmatical. They are usually attached by dichotomously 

 branched gelatinous stalks to algse, stones, leaves of water-plants etc. Some forms are inbedded 

 in gelatinous masses, but frustules of attached species occur also occasionally free. 



Artificial key. 



1. Stigmatica. 



( Median stri 



I L. 0,1 

 \ L. 0,0 



•I 



striae alternately longer and shorter . 

 not — — — 



L. 0,1 to 0,12 mm. . .... 



5 mm. ... 



{Axial area distinct or broad . . 



- — indistinct or narrow . . 

 {Area linear 

 — lanceolate ... 



Ends subacute or apiculate . . .... 



7. 

 8. 



10. 

 11 



12. 



■r 



broadly truncate .... .... 



( Striae about 12 in 0,i mm. 



^- i ^ - 8 - , . 



J Central area transverse . . 



\ — — small and rounded or indistinct 



J Central area unilateral ... ... 



' \ — — bilateral .... . ... 



{Ends apiculate ... .... 



— rostrate to truncate .... ... 



— broad, rounded-truncate . .... 



{Central area narrow 

 — — broad .... 



Striae coarsely punctate . . 



obscurely — 



J Valve biconstricted . G. acuminatum Ehb. (O. 



\ — not — . . . ... 



[ Ends capitate . . . 



13. ■! • — • apiculate . 



I — rounded ... 



... ( Striae coarsely punctate . . . . . . • 



\ — finely or obscurely — ... 



G. geminatum Ltngb. 

 G. constrictum Ehb. 

 4. 

 7. 

 5. 

 6. 



■ G. validum Cl.. 



. G. Berggrenii Cl. 



. . . Gr. ventricosum Greg. 



. . G. oxycephalum Cl. 



. ' . . 8. 



. . 12. 



9. 



10. 



G. Augur Ehb. 



. . . G. angustatum Kutz. 



. . . G. subtile Ehb. 



G. gracile Ehb. 



11. 



. . Gf. semiapertum Gkun. 



...(?. intricatum KtiTZ. 



subelavatum var. Mnstela). 



13. 



G- sphmrophorum Ehb. 

 . . G. apicatum Ehb. 

 .... 14. 

 . . . Gf. lanceolatum Ehb. 

 15. 



* G. cantalicum Br. a. H^rib. 



