STAURA STRUM. 175 



recorded by many authors, ourselves included, ns a distinct 

 variety. Careful examination of large numbers of specimens 

 has convinced us, however, that the angles of this species are 

 never more than subtruncate, and that every state exists 

 between those which are subtruncate and those which are 

 entirely rounded. We are therefore compelled to discard the 

 var. obtusilobum, as it is founded upon a character which c;ni 

 only be regarded as slight, indefinite, and arbitrary. 



The description given by Roy and Bissett of the zygo- 

 spore requires confirmation. From their figure (in ' Ann. 

 Scott Nat. Hist/ 1894, t, 4, f. 4) we should say that it is very 

 similar to the zygospore of the closely allied species St. 

 striolatum, in which case it would be compressed and not 

 " barrel-shaped." The outlines of the semicells as depicted 

 by Messrs. Roy and Bissett do not agree with those of St. 

 dilatatum. 



Cushman (in 'Ball. Torr. Bot. Club/ xxxii, 1905, p. 227, 

 t. 8, f. 14) has also described and figured what he considers 

 to be the zygospore of St. dilatatum. His description states 

 that it is "elliptical, covered with rounded protuberances/ 7 and 

 his figure, although somewhat poor, might possibly be recon- 

 ciled with an oblique view of a zygospore similar to that of 

 St. ttriolatum (cf. PI. CXXVII, fig. 5). 



The Desmid described by Boldt (' Desm. Gronland/ 1888, 

 p. 37, t. 2, f. 48) under the name of "St. inargaritaceum var. 

 truncatum 3 ' is a variety of St. dilatatum "with truncate apices, 

 and should be placed as St. dilatatum var. TBUNCATUM. 



Var. hibernicum nob. (PI. CXXVI, fig. 18.) 



St. sinense Liitkem. var. liibernicum W. & G. S. West, Alg. X. Ireland, 

 1002, p. 52, t, 2, f. 34. 



Cells rather small, basal portion of semicells more 

 pronounced ; granules very minute, disposed in series 

 around the angles but irregularly scattered on the rest 

 of the cell. 



Length 24^; breadth 21-24 /x; breadth of isthmus 



7 



IRELAND. Louo'h Anna, Donegal ! 



o o 



This Desmid was originally described as a variety of St. 

 sinense, but the convex apex of the semicells, combined with 

 the fact that the cell is finely granulate all over, points 

 unmistakably to a close relationship with St. dilatatum. 



