STAURASTRUM. 125 



oblong-elliptic, the ventral margin more convex than 

 the dorsal, angles produced to form short, stout, diverging 

 processes, externally smooth, and quite solid, with deeply 

 bifurcated apices. Vertical view triangular, sides slightly 

 concave, angles produced to form short solid processes, 

 bifurcate at the apex. Cell-wall covered with granules 

 arranged in about 4 distant series round the angles, 

 minutely punctate between the granules. 



Zygospore unknown. 



Length, without spines, 34-40 pi ; breadth, without 

 spines, 38-47 pi ; with spines, 64-75 u ; breadth of 

 isthmus 12'5-13pi. 



SCOTLAND.- -Plankton of the Orkneys and Shetlands ! 



IRELAND.- -Plankton of Lough Corrib, Galwav ! Louoii 



1 O 



Neagh ! Lough Beg, Londonderry ! 



Geogr. Distribution. Sweden (form). Iceland (form). 



This species, which only occurs in plankton, is perhaps nearest 

 to St. Avicula Breb. It differs from that species, however, in 

 its much larger size and in the peculiar, solid, deeply bifurcate 

 processes, which are directed slightly upwards. The two spines 

 of St. Avicula are attached more or less independently to the 

 body of the Staurastrum, whereas the much larger spines of St. 

 pelagicum are the two divisions of a very deeply divided but 

 solid process. It is also closely allied to St. pseu(lopelagic"/n 

 W. & G. S. West, but is distinguished by its more elliptical 

 semicells and solid processes. The processes of St. pseudo- 

 pelagicum are hollow, but the terminating spines of the two 

 species are very similar. 



130. Staurastrum polymorphum Breb. 

 (PI. CXLII, fig. 24 ; PL CXLIII, figs. 1-3.) 



St. polymorphum Breb. in Ralfs, Brit. Desm. 1848, p. 135, t. 22, f. 9, t. 34, f. G ; 

 Arch, in Pritch. Infus. 1861, p. 742, t. 2, f. 20, 21, 24, 25, 31 ; Rabenh. 

 Krypt.-fl. Sachs. 1863, p. 192 ; De Not. Desm. Ital. 1867, p. 52, t. 4, f. 46 ; 

 Rabenh. Flor. Europ. Alg. 1868, p. 209 ; Delp. Spec. Desni. subalp. 

 1877, p. 162, t. 11, f. 56-62 ; Kirchn. Alg. Schles. 1878, p. 167 ; Wille, 

 Ferksv. Alg. Nov. Semlj, 1879, p. 53 ; Wolle, Desm. U. S. 1884, p. 126, 

 t. 42, f. 9, 10, 24, 25 ; Cooke, Brit. Desm. 1887, p. 169, t. 58, f. 4 ; Boldt, 

 Desm. Gronland, 1888, p. 38 ; Hansg. Prodr. Alg. Bohm. 1888, p. 213 ; 

 De Toni, Syll. Alg. 1889, p. 1208 ; Anderss. Sverig. Chlor. 1890, p. 12 ; 

 Giitw. Flor. Glondw Okolic Lwowa, 1891, p. 68; Flor. Glonow Galic. 



