90 BRITISH DESMIDIACE^. 



normally be slightly retuse or emarginate, but they are often 

 truncate with a median papilla, or even bluntly triangular. 

 There is also a great tendency for the lateral lobes to grow in 

 size until they not only overlap each other at the sinus, but 

 also overlap the polar lobe on each side. 



Var. hamata Wolle. (PL XLIII, figs. 10, 11.) 



M. conferta var. hamata Wolle, in Bull. Torr. Bot. Club, 1883, p. 19, t. 27, 

 f . 1 '; Desrti. U. S. 1884, p. 114, t. 53, f. 12, 13 ; West & G. S. West, 

 Some N. Amer. Desni. 1896, p. 241, t. 14, f. 8, 9. 



M. hamata Borg. Desm. Bras. 1890, p. 31. 



Lateral lobes as in the typical form, or rarely some- 

 what further subdivided; polar lobe less widely 

 cuiieate, with the lateral angles downwardly uncinate. 



Length 80-128 ^ ; breadth 75-107 ^ ; maximum 

 breadth of polar lobe 3 6' 5-53 ^ ; breadth of isthmus 

 10-5-19 p. 



SCOTLAND. Plankton of Loch nan Cuimie, Suther- 

 land ! (J. Murray). K"ear Tarbert, Harris, Outer 

 Hebrides ! 



Geogr. Distribution. United States. 



This is a very curious variety of M. conferta in which the 

 lateral margins of the polar lobe are greatly excavated just 

 below the angles of the lobe. The lobe is thus more or less 

 anvil-shaped, and the angles are distinctly uncinate. The 

 incisions below the polar lobe are therefore widely open, but 

 closed again at the outer extremity.' Specimens of this variety 

 sometimes reach a larger size than is ever attained by the 

 typical form. 



We have already pointed out (' Some N". Amer. Desm./ 

 p. 241) that Borgesen. was greatly in error in elevating this 

 variety to the rank of a species. Moreover, the Micrasterias 

 which Borgesen figured from Brazil under the name of 

 " M. hamata forma Brasiliensis ' (vide Borg. ' Desm. Bras/ 

 t. 2, f. 11) is certainly not a form of M. conferta var. hamata. 

 We have seen many specimens of M. conferta which combined 

 the characters o both the type and the var. hamata. Very 

 often the polar lobe of one semicell is typical, whereas that of 

 the other semicell is such as is found in the var. hamata. We 

 give a figure of one of these forms which demonstrates con- 

 clusively that the var. hamata is truly a variety of- AT. conferta 

 and not a distinct species (PL XLIII, fig. 9 ; length 77 ^t ; 

 breadth 76 



