MK'KASTEKLAS. 89 



ginate (sometimes convex with a median papilla). 

 Side view of semicell rectangular-oblong, apex rounded- 

 Truncate and bearing o papillae, sides slightly retuse. 

 Vertical view oblong-lanceolate with a papilla at each 

 pole. Cell-wall minutely punctate. 



Zygospore unknown. 



Length 84-89 ^ ; breadth 74-82 p ; breadth of polar 

 lobe 40-44 p.; breadth of isthmus 1(3-19 p.; thickness 



o^> 



-0 fJi. 



SCOTLAND.- -Glen Urquhart, Inverness; Upper Pow- 

 lair in Birse, Birsemore Loch, Dalwhing near Aboyne, 

 near Loch Dawan, and near Loch Kinord, Aberdeen ; 

 Muiryhaugh and Dalbrake in Strachan, Kincardine; 

 Glen* Coe, Argyll ; Xorth Glen Sannox, Arran (Eoij fy 

 Bissetfy. Xear Stirling! Ehiconich, and plankton of 

 Loch Morar, Sutherland ! Xear Tarbert and in the 

 plankton of Loch Laxadale, Harris ! Xear Balallan and 

 in plankton of Loch Mor Bharabhais, Loch Cuthaig, 

 and Loch Fadaghoda, Lewis, Outer Hebrides ! 



Geogr. Distribution.- -France. Xorway. Sweden. 

 Finland. Greenland. United States. 



This Micrasterias is essentially of a northern type and it is 

 one of the rarest British species. In Europe it seems to be 

 almost confined to the north-western countries,, and it is met 

 with frequently in the eastern parts of the United States. 



It is only known from Scotland in the British Islands, 

 having 1 been found in a number of localities on both the 



^j 



eastern and western slopes. In some parts of the Outer 

 Hebrides it can be obtained frequently, "but never in abundance. 



J/. conferta is a very characteristic species, 3/. papillifera 

 being the only other species of the genus with which it could 

 be confused. It is, however, easily distinguished hy the 

 shortness and breadth of the polar lobe, which widens out 

 from a relatively narrow base. The lohes and lohules are 

 more compact and crowded than is generally the case in 

 31. papillifera, and the incisions between them are not so 

 deep. The apex of the polar lobe also differs greatly from 

 that of M. papillifera, and the interlobular incisions are not 

 bordered hy minute spines. 



Irregularities in the form of the lobules are of frequent 

 occurrence. The four small lohules of each lateral lobe should 



