BRITISH DESMIDIEyE. 19/ 



6. MiCRASTERIAS. 



1 . Lobes of segments radiate, incised and cuneate 2 



Lobes horizontal, tapering and bidentate 12 



2. Frond orbiciUar or oblong ; lobes and subdivisions approximate .... 3 

 Frond subelliptic ; end lobe exserted 10 



3. Frond oblong Jenneri. 



Frond orbicular 4 



4. End lobes broadest 5 



End lobes narrow 6 



5. End margin convex crenata. 



End margin truncate or concave truncata. 



6. Principal divisions of the frond bordered with puncta-like 



granules papillifera. 



Surface of frond smooth , 7 



7. Ultimate subdivision of lateral lobes inflated and tapering .... radiosa. 

 Ultimate subdivisions tnmcate 8 



8. Extremities of subdivisions neither spinous nor mucronate. . denticulata. 

 Extremities of subdivisions either spinous or mucronate 9 



9. Extremities of subdivisions abrupt with acute or spinous angles. . rotata. 

 Extremities of subdivisions rounded and furnished with two 



mucros Jimbriata. 



10. Angles of end lobe bipartite ; lateral lobes toothed americana. 



Angles of end lobe bidentate ; lateral lobes deeply divided 11 



1 1 . Subdivisions of lobes long, narrow-linear furcata. 



Subdivisions of lobes short, scarcely linear Crux-Melitensis. 



1 2. End margin convex ; lobes conical oscitans. 



End margin straight ; lobes triangular pinnatifida. 



7. EUASTRUM. 



1 . Terminal lobe distinct, cuneate, included in a notch formed 



by the lateral lobes 2 



Terminal lobe exserted or indistinct 4 



2. Frond rough ; end margin sinuated verrucosum. 



Frond smooth ; terminal notch linear 3 



3. Segments 5-lobed oblongum. 



Segments 3-lobed crassum. 



4. Segments vdth a distinct, narrow, terminal notch 5 



Segments with the end margin straight or slightly concave 15 



o 2 



