DESMID FLORA OF DARTMOOR. 263 



Fig. 2. Euastrum (monstrosity) from Teignhead bog. The lower 

 semi-cell of this plant is typical Euastrum Didelta (Turp.) 

 Ralfs, while the upper semi-cell if not Euastrum humero- 

 sum Ralfs is a very close approximation, x 300. 



3. Euastrum affine Ralfs, forma scrohiculata Nordst. See 

 note (105) p. 259. x 510. 



4. Euastrum pictum Borg. forma, x 510. 



5. Euastrum crassum (Breb.) Kutz. var. scrobiculatum 

 Lund. 



6. Euastrum ohlongum (Grev.) Ralfs. Specimen in hyaline 

 case. X 300. 



7. Euastrum hinale (Turp.) Ehrenb. forma secta Turner. 

 This form differs considerably in having the basal lobes 

 sub-quadrate and a deeper incision between the basal 

 and polar lobes, x 510. 



8. Euastrum duhium Nag. var. nov. 27 //, x 18 /x. This 

 variety appears to be a much reduced form, with the 

 lobulation of the basal lobes less developed and the 

 conical granules of the polar lobe wanting, x 510. 



9. Cosmarium suhquadratum Nordst. x 510. 

 10. Cosmarium formosulum Hofi. x 510. 



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Plate 19. 



Fig. 1. Cosmarium ornatum Ralfs form, x 510. 

 ,, 2. Cosmarium hipunctatum (Borg.) forma subrectangularis 

 West. The central papillae in most of the Dartmoor 

 specimens are larger than in typical C. hipunctatum and 

 divided transversely, so that they almost appear as 

 four. X 510. 



3. Cosmarium lepidum West. var. x 510. 



4. Cosmarium venustum (Breb.) Arch. " An unusual 

 form," Professor G. S. West, x 510. 



5. Staurastrum Bieneanum Rabenh, form with markedly 

 retuse apices, x 510. 



6. Arthrodesmus Incus Breb. var. Ralfsii West. Monstrous 

 form, with development of additional semi-cell. A 



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