STAURASTRUM. 109 



Cells small, about Ij times broader than long, includ- 

 ing the processes, deeply constricted, sinus rectangular, 

 widely open ; semicells subcuneate. ventral margin 

 tumid, much more convex than the dorsal, semicells 

 gradually attenuated at the angles to form long, slender, 

 slightly incurved processes, tipped with 2 or 3 very 

 minute spines and provided with several concentric 

 series of minute denticulations. Vertical view triangular, 

 sides concave, angles produced into slender denticulate 

 processes, and with a row of tiny granules just within 

 each lateral margin. Cells often twisted about the 

 isthmus, so that the processes of one semicell alternate 

 with those of the other. 



? Zygospore spherical, with numerous slender pro- 

 cesses twice dichotomous at the apex.* 



Length 21 '7-26(1 ; breadth, without processes, 14-15 a ; 

 including processes, 30-40 ^ ; breadth of isthmus 5-7*5 (JL. 



ENGLAND.- \Yestmoreland ! (Biss.), and in the plank- 

 ton of Codale Tarn ! Lancashire ! W. & N. Yorks ! 

 Cheshire and Leicester (Roy). Essex ! Cambs ! 

 Warwicks ! and in the plankton of Bracebridge Pool, 

 Sutton Park ! Worcester ! Surrey ! Kent ! Hants ! 

 (Roy). Devon ! (Harris). Cornwall ! 



WALES. Snowdon !, Capel Curig ! (Cooke & Wills] y 

 and Llyn Ogwen !, Carnarvonshire. Llyn Coron, Angle- 

 sea ! Ffestiniog, Merioneth ! 



SCOTLAND. General ! (Roy & Biss.}. Near House of 

 Hill, Wigtown ! Orkneys and Shetlands ! 



IRELAND. Donegal ! " Clare Isle, Mayo ! Galway ! 

 Kerry! Dublin and Wicklow (A rch.). Down! London- 



V 



derry 1 



Geogr. Distribution.- -France. Germany. Switzerland. 

 Galicia in Austria. Portugal. Norway. Japan. 



St. inflexum is a much commoner species than its ally St.. 



* Amongst the papers of the late Professor West is a drawing of a zygospore 

 by the late Dr. Lutkemiiller, who suggests that it is possibly St. brachycerum 

 From a study of the empty semicells surrounding the zygospore, however the 

 writer is inclined to attribute it to St. inflexum Breb. It was of 

 described above (see PI. CLXVII, f. 7). 



