176 BRITISH DESMIDIACE&. 



33. Staurastrum disputatum nov. now. 

 (PL CXXVI, fig. 16; PL CXXIX, fig. 1.) 



St. dilatatum var. insigne Racib. Desmidyja Ciastonia, 189^, p. 388, t. 1, 

 f. 13 ; W. & G-. S. West, Welw. Afric. Fresh w. Alg. 1897, p. 18 L [forma 

 minor] ; Borge, Alg. erst. Kegnell. Exped., II. Desmid. 19U3, p. 107, 

 t. 4, f. 12 [forma minor]. 



Cells small, a little longer than broad, moderately 

 constricted, sinus widely open and obtuse-angled, with 

 the apex minutely acuminate ; semicells \videly cunei- 

 form from a broad base, lateral margins slight! v retuse, 



O O / 



apex widely truncate and flat, angles slightly produced 

 and rounded. Vertical view quadrangular, angles 

 somewhat produced and rounded, sides concave. Cell- 

 wall granulate at the angles, but the body of the cell 

 (including the apices) quite smooth, granules disposed 

 in 4 or 5 rings around the angles. 



Zygospore unknown. 



Length 35 //, ; breadth 33 ^ ; breadth of isthmus 

 19 p.. 



IRELAND.- -Near Westport, Mayo! Lough Bofin, 

 Gralway ! 



Geoqr. Distribution. W. Africa. Brazil. Argentina, 



if O 



It does not seem to us quite correct to place this Desmid as 

 a variety of St. dilatatum. It differs from that species verv 



a/ / 



much iu the form of its semicells and in its granulation. The 

 sinus is more widely open, the apex of the semicell is very 

 widely truncate and straight, and the granules are confined 

 to the angles, around which they are disposed in four or five 

 series. Under these circumstances we have established it as 

 a species. Neither " insigne ' nor " Raciborskii ' could be 

 utilized for the specific name, as both are already in use. 



Borge has mentioned a " forma minor } from Brazil : 

 length 20-21 /u; breadth 20-21/1; breadth of isthmus 9^. 

 We recorded this same small form from West Africa in 1897. 



The following might also be best regarded as varieties of 

 this species : 



Var. SINENSE (Lutkem.) nob. St. sinense Liitkem. Desm. 

 Central China, 1900, p. 124, t. 6, f. 39, 40 ; G. S. West, Alg. 

 Third Tanganyika Expedit. 1907, p. 125. Cells smaller, body 



