192 BRITISH DESMIDIACE^:. 



narrowly elliptic, ratio of axes about 1 : 1*8. Cell- wall 

 smooth. 



Zygospore unknown. 



Length 19' 5 //, ; breadth 13*5 JJL ; breadth of isthmus 

 4 p. ; thickness 6' 5 /A. 



ENGLAND. Louolirio-o- Westmoreland ! 



o o o ' 



Geogr. Distribution. United States (Colorado). 



This small species is principally distinguished from C. 

 atlanthoideum Delp. in being relatively narrower, and in the 

 narrowly-elliptic vertical view without any trace of a median 

 inflation. 



43. Cosmarium subtumidum Xordst. 

 (PL LXIII, figs. 18-20.) 



Cosmarium subtumidum Nordst. in Wittr. & Nordst. Alg. Exsic. 1878, 

 no. 172 ; 1889, fasc. 21, p. 44 cuni fig. xylogr. ; Hansg. Prodr. Algenfl. 

 Bohm. 1888, p. 249 ; Boldt, Desmid. Gronland, 1888, p. 16 ; De Toiii, 

 Syll. Alg. 1889, p. 950 ; West, Alg. K Wales, 1890, p. 288 ; Alg. Eng. 

 Lake Distr. 1892, p. 725; Eoy & Biss. Scott. Desm. 1894, p. 175; 

 Nordst. Index Desni. 1896, p. 248 ; West & a. S. W T est, Alg. S. England, 

 1897, p. 485 ; Alga-fl. Yorks. 1900, p. 69 ; Alg. N. Ireland, 1902, p. 33. 



Ursinella subtumida Kuntze, Eevis. gen. plant. 1891, p. 925. 



Cells small, about ly times as long as broad, deeply 

 constricted, sinus very narrow with a dilated apex; 

 semicells pyramidate-semicircular, basal angles round- 

 ed, lateral margins convex, apex widely truncate and 

 generally straight. Side view of semicell circular. 

 Vertical view elliptic, sometimes with the rounded 

 poles very slightly produced, ratio of axes 1 : 1*84. 

 Cell-wall minutely punctate. Chloroplasts axile, with 

 one pyrenoid. 



Zygospore globose and spiny, spines obtuse. 



Length 30-40 ju,; breadth 26-33 p. ; breadth of 

 isthmus S-10'5 //, ; thickness 17-19 /x; diam. zygosp. 

 without spines 30-32 JLC, with spines 44-51 ^ ; length 

 of spines 6-12 ^ ; thickness of spines 3-5 p. 



ENGLAND.- -Westmoreland ! W. and N. Yorks ! 

 Surrey ! Kent ! Cornwall ! 



WALES. Llyn Pencraig near Bettws-y-coed, Llyn 

 Bodgynwydd, Moel Siabod, Llyn Bochlwyd, Llyn-y- 



