STAURASTRUM. 9 



species and, at the same time, it is somewhat variable in form 

 and in the inflexion of its spines. These are usually inserted near 

 the apex of the semicell and are, as a rule, slightly divergent 

 or parallel. The more or less triangular form of the semicells 

 and the dorsal insertion of its spines are the features by which 

 it can be distinguished from St. mucronatum. In the latter 

 species the semicells are more elliptical in form and the spines 

 are lateral in their insertion. 



There has been much confusion in the past between St. dejec- 

 tum and St. mucronatum, particularly with regard to the zy go- 

 spores. Kalfs (in ' Brit. Desm.' 1848) united the two species 

 and figured them under the name of St. deject um. The con- 

 jugating specimens figured by him belong most probably to St. 

 mucronatum., as is evident from the shape of the semicells (see 

 ' Nordst. Freshw. Alg. N. Zeal.' 1888, p. 40). These zygospores 

 have been copied by many authors and reproduced under the 

 name of St. dejection. The zygospore of St. dejection is, however, 

 not well known, since it has only been figured by De Bary (' Conj.' 

 1858, t. 6, f. 26-32) and Eeinsch (' Contrib. Alg. Fung.' 1875, 1. 15, 

 f. 8). 



Forma major West & G. S. West. (PL CXXIX, fig. 13.) 



Stauraslruni dejectum forma West & G. S. West, Comp. Study Plankton 

 Irish Lakes, 1900, p. 102, t. 11, f. 1(3. 



Differs from the type in its larger size and much 

 stouter spines. 



Length, without spines, 42 pt ; breadth, without spines, 

 48 pi ; breadth, including spines, 80-85 u ; breadth of 

 isthmus 11 (JL. 



IRELAND.- -Plankton of Lough Corrib, Galway ! 



Var. patens Nordst. (PI. CXXX, figs. 1, 2.) 



Stanrasfnun dejectum /3 patens Xordst. in Botan. Xotis. 1887. p. 158 ; Freshw. 

 Alg. N. Zeal. 1888, p. 39, t. 4, f. 16 ; De Toni, Syll. Alg. 1889, p. 1138; 

 \Vest, Alg. Engl. Lake Distr. 1892, p. 18 ; Borge, Siisswasseralgen Siid- 

 Patagon. 1901, p. 27, t. 1, f. 11 ; Gutw. Flor. Alg. Mont. Tatr. 1909, 

 p. 470 ; Borge, Sao Paulo Siisswasseralgen, 1918, p. 47. 



A form with small spreading spines which are diver- 

 gent ; sinus acute-angled, isthmus not even slightly 

 elongated. 



