KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 26. N:() 2. 125 



1. B. Boeckii Ehb. (1838). — Frustule stiijitate. V. lanceolate. L. 0,12; B. 0,023 mm. 

 Central nodule elongated. Terminal fissures straight, at a short distance from the ends. Strise 10 

 (middle) to 13 (ends), radiate at the ends. Pimcta of the exteriör stratum forming fine lineolse, 

 about 30 in 0, 01 mm. — Cocconema Boeckii Ehb. Inf. Pl. XIX f. 5. Doryphora BoecJcii W. Sm. 

 B. I). Pl. XXIV f. 223. Brvhissonia Boeckii Grun. Verh. 1860 p. 512. 



Brackish water: Baltic (from Roslagen and Bay of Finland to Kiel)! Coasts of England! 

 Connecticut to North Carolina! 



Var. minor Cl. — L. 0,o58; B. 0, 01 6 mm. Strise in the middle 12, at the ends 15 in 0, 01 mm. 



Brackish water: Amsterdam (Kinker CoU.)! 



Ampliipleura Kutz (1844). 



Valve elongated, fusiform or linear, withoiit longitudinal lines or ridges. Central nodule 

 elongated into a rib, extending throughout the whole valve, furcate towards the ends. Struc- 

 ture: very fine puncta arranged in parallel, transverse and straight longitudinal striae. Cell- 

 contents: two endochrome-plates along the inside of the connecting zone. Median plasma-mass 

 distinct. On conjugating two cells give origin to two auxospores (»Berkeleya Dillwynii» Lliders 

 Beob. p. 59). 



The genus Awphipleura was founded in 1844 by Kutzing (Bac. p. 103) for Frustnlia peUu- 

 cida, known already by him in 1833. Nitzchia Sigma, under the name of Amphipleura rigida, was 

 also included in the new genus. According to Kutzing and all låter authors (compare the ideal 

 section in Van Heurck synopsis Pl. XVII f. 14 A) the valve of Amphipleura has on both sides of 

 the axis an elevated line or ridge, which I have always failed to discover. Certain small forms 

 of Amphipleura live in gelatinous tubes, and for these the genera BerJcelcya Grev. (1827), Rhaphi- 

 dogloea (Kutz. 1844) were founded. They have also been included in Scimonema, Micromega, 

 Bangia, Monema. Conferva etc, but there is no more reason for separating these forms from Amphi- 

 pleura thau for distinguishing Encyonema, Endosigma, Endosfauron, Schisonema and Colletonema 

 from Cymhella, Gyrosigma, Navicula and Frustulia. The frustules of the forms living in tubes 

 are exactly similar to those of the true Amjihijjleura, only smaller. The shape of the gelatinous 

 tubes is in my opinion of little importance. Grunow in 1880 (Bot. Centralblatt) wrote an elaborate 

 monograph of these forms, to which 1 refer. 



The diatoms most nearly akin to Amphipleura are to be found in the genus Frustulia. In 

 this genus one meets with forms, having a small central nodule and obscure median line, enclosed 

 between two, strong interiör silicious ridges, forming at the ends of the valve a aporte-crayon»- 

 shaped figure. In some forms the central nodule becomes fused together with the silieeous ridges. 

 If the fusion extends farther, we get the forms of the central nodule, eharacterizing AmphipÅeura. 

 The »forks» in Amphipileiira correspond to the ^port-crayons» in Frustulia and to the »horns» in 

 Diploneis. Another genus, to a certain degree akin to Amphip)leiira is Brebissonia. Perhaps the 

 curious and isolated Hydrosilicon Brun^ (Amphijjrora rimosa, 0'Meära) may be a distant relative. 

 Amphipleura Dehyi appears in some respects to be intermediate. 



AU species of Amphipleura, except A. Debyi, are nearly related, have the same important 

 characteristics, and differ only in the size, some slight diiferences in the outline, the length of 

 the forks, and number of striee. They inhabit fresh as well as brackish or salt water. Fresh- 

 water forms are larger, live free or enclosed in mucous, amorphous masses, the marine live enclosed 

 in tubes. Of the freshwater-forms those living in warmer or tropical countries are the largest 

 and in structure coarsest. 



