STAURASTRUM. 43 



Geogr. Distribution. - Germany. Austria (form). 

 Servia. Switzerland. Norway. 



This species is readily distinguished from St. Aricula by its 

 finer granulation, and by the fact that the angles of the semi- 

 cell are produced to form distinct cylindrical processes. St. 

 Avicula var. subarcuatum forms, in some ways, a connecting 

 link between the two species. By reason of its almost cylin- 

 drical processes, St. subcruciatum might well be considered a 

 member of Section I. 



SECTION F. 



Cells provided with numerous spines, either clothing the whole 

 surface of the cell-wall, or more or less restricted to the vicinity of 

 the angles. 



* Spines few in number or restricted to the vicinity of the 

 angles, semicells sometimes with an apical series of spines 

 as well. 



70. St. pungens. 



71. St. Simonyi. 



72. St. cristatiim. 



73. St. oligacanihum. 



74. St. trachygonum. 



75. St. spimferum. 



76. St. Picum. 



77. St. horametrum. 



** Spines numerous and more or less distributed over the whole 



surface of the cell. 



| Spines of considerable length and of two very distinct 

 kinds, a few at the angles being considerably stouter 

 than the rest. 



78. St. setigerum. 



"j"j~ Spines all more or less similar, or becoming gradually 



longer towards the angles. 



J Semicells broadly oval or rhomboidal, cells dis- 

 tinctly longer than broad, with an open sinus. 



79. St. polytrichum. 



80. St. saxonicum. 



81. St. cumbricurn. 



82. St. 



