130 BEITISH DESMIDIACE^. 



{J Cells l|-lf times longer than broad. 



47. C. canaliculatum. 



48. C. pyramidatum. 



49. C. pseudopyramidatum. 



50. C. variolatum. 

 ** Margin of semicells undulate or crenate. 



t Semicells constricted and crenate just below the apices. 



51. C. Holmiense. 



52. C. cymatopleurum. 



ft Semicells with the lateral margins undulate or crenate. 

 J Apex of semicells without undulations. 



53. C. obtusatum. 



54. C. venustum. 



55. C. Garrolense. 



56. C. Reinschii. 



+ * Apex of semicells often slightly undulate. 



57. C. Nagelianum. 



58. C. notabile. 



59. C. tetragonum. 



SECTION D. Semicells circular or subcircular (rarely almost 

 semicircular) in outline. 



* Constriction fairly deep. 



60. C. moniliforme. 

 ** Constriction slight. 



f Margin of semicells entire. 



J Cells large or of medium size (47-102 p in length). 



61. C. alpestre. 



62. C. comiatum. 



63. C. pseudoconnatum. 

 {{ Cells small (15-34 /x in length). 



64. C. globosum. 



65. C. subarctoum. 



66. C. pseudarctoum. 

 ft Margin of semicells undulate. 



67. C. pericymatium. 



SECTION E. Semicells more or less rectangular or subrect- 

 angular (rarely subpyramidal). 



* Margin of semicells crenate or undulate. 



t Cells minute, sinus widely open. 



68. C. Nov& Semli&. 



69. C. Regnesi. 



70. C. cymatonotopliorum. 

 ft Cells larger, sinus linear. 



71. C. rectangulum. 

 ** Margin of semicells entire. 



f Constriction very slight. 



72. C. arctoum. 



