KONGL. SV. VET. AKADEM1EN8 HANDLINGAR. BAND 26. N:0 2. 125 



1. B. Boeckii Ehb. (1838). — Frustule stipitate. 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. Puncta of the exterior stratum forming fine lineolse, 

 about 30 in 0,oi mm. — Cocconema Boeckii Ehb. Inf. PL XIX f. 5. Doryphora Boechii W. Sm. 

 B. D. PI. XXIV f. 223. Brebissonia Boechii Gkun. Verh. 1860 p. 512. 



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

 Connecticut to North Carolina! 



Var. minor Cl. — L. 0,058; B. 0,oi6 mm. Strise in the middle 12, at the ends 15 in 0,oi mm. 



Brackish water: Amsterdam (Kinker Coll.)! 



Amphipleura Kutz (1844). 



Valve elongated, fusiform or linear, without 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» Liiders 

 Beob. p. 59). 



The genus Amphipleura was founded in 1844 by Kutzing (Bac. p. 103) for Frustulia pellu- 

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

 also included in the new genus. According to Kutzing and all later 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 Berkeleya G-rev. (1827), Rhaphi- 

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

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

 pleura than for distinguishing Encyonema, Endosigma, Endostauron, Schizonema and Colletonema 

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

 are exactly similar to those of the true Amphipleura, 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 I 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 interior silicious ridges, forming at the ends of the valve a »porte-crayon»- 

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

 If the fusion extends farther, we get the forms of the central nodule, characterizing Amphipleura. 

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

 Diploneis. Another genus, to a certain degree akin to Amphipleura is Brebissonia. Perhaps the 

 curious and isolated Hydrosilicon Brun, (Amphiprora rimosa O'Mbara) may be a distant relative. 

 Amphipleura Debyi appears in some respects to be intermediate. 



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

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

 the forks, and number of strise. 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. 



