186 BRITISH DESMIDIACE^l. 



[= St. j)ygm3Biim var. trilineatum West,, ' Alg. W. Ireland/ 

 1892, p. 177, t. 23, f. 7]. 



"St. pygm&vm var. obtusum 3 Wille ('Ferskv. Alg. Nov. 

 Semlj/ 1879, t. 13, f. 56) appears to be more closely related to 

 St. hexacerum (Ehrenb.) Wittr. 



Var. striatum var. nov. (PI. CXXVIII, figs. 5, 6.) 



St. pygmseum as figured by W. & GK S. West, Notes Alg. II, 1900, p. 297, 

 t. 412, f. 12. 



Semicells more distinctly rhomboid than in the type; 

 granules most minute, fewer in number, and arranged 

 in somewhat distant series around the angles. Zygo- 

 spore exactly like that of var. pijcjnidewm. 



Length 29-31 /x; breadth 29-31 '5 /x; breadth of isth- 

 mus 9'5-11'5/x; diam. zygosp. without spines 36-37/x,, 

 with spines about 67/x. 



ENGLAND. --Cautley Spout, AY. Yorks (with zy go- 

 spores) ! 



This is the most angular of any of tlie varieties of St. 

 punctulatum. It is well characterized by its somewhat distant 

 lines of granulations. 



Two other forms of St. punctulatum, although not yet found 

 in the British Islands, require brief mention. 



Forma KLLIPTICA Lewin, Span. Siisswasseralg. 1888, p. 9, 

 t. 1, f. 16. Semicells rather narrowly elliptic; length 24*6- 

 26-6 M ; breadth 25'2-29'3/x; breadth of isthmus S'7-9'3/i. 

 Distrib. Spain. We have seen nothing precisely like this 

 form, and think that it may possibly belong to St. alternant*. 



Var. MURICATIFORME Schmidle, Lappmark Siisswasseralgen, 

 1898, p. 57 \_= St. muricatiforme Schmidle, Beitr. alp. Alg. 

 1895, t. 16, f. 14, 15 ; 1896, p. 162]. Cells with a less open 

 sinus; semicells elliptic-subsemicircular, granulation less dense 

 than in the type; angles in the vertical view more rounded. 

 Length 28-32 /u; breadth 23-30 /m. Schmidle has described a 

 "forma lapponica" of this variety which very nearly approaches 

 St. punctulatum f. elliptica Lewin. We have not observed 

 var. muricatiforme from any part of the British Islands, and 

 as originally described by Schmidle it appears to be known 

 only from the Tyrol. 



