MICRASTERIAS. 105 



12. Micrasterias denticulata Breb. 

 (PI. XLIX, figs. 1-7 ; PI. L, figs. 1, 2.) 



Micrasterias denticulata Breb. Alg. Falaise, 1835, p. 5-4, t. 8 ; Ralfs, Brit. 

 Desm. 1848, p. 70, t. 7, f . 1 ; De Bary, Conj. 1858, p. 41 ; Arch, in Pritch. 

 Infus. 1861, p. 727, t. 2, f . 22 ; in Quart. journ. Micr. Sci. 1867, p. 296 ; 

 1. c. 1868, p. 294 ; Rabenh. Flor. Europ. Alg. Ill, 1868, p. 108, cum fig. 

 xylogr. ; Lund. Desm. Suec. 1871, p. 12 ; Jacobs. Desni. Danem. 1875, 

 p. 186, t. 7, f. 11, t, 8, f. 1 ; Kirchn. Alg. Schles. 1878, p. 162; Gay, 

 Monogr. loc. Conj. 1884, p. 52, t. 1, f . 2, 3 ; Wolle, Desm. U. S. 1884, 

 p. 109, t. 34, f. 4-8 [forms] ; Cooke, Brit. Desm. 1886, p. 56, t. 22 ; 

 Hausg. Prodr. Algenfl. Bohni. 1888, p. 209 ; De Toiii, Syll. Alg. 1889, 

 p. 1130; West, Alg. N. Wales, 1890, p. 286; Alg. W. Ireland, 1892, 

 p. 134 ; Alg. Eng. Lake Distr. 1892, p. 722 ; Roy & Biss. Scott. Desm. 

 1893, p. 174 ; Nordst. Index Desm. 1896, p. 99 ; West & G. S. West, 

 Alg. S. England, 1897, p. 484; G. S. West, Variation Desm. 1899, p. 384 ; 

 West & G. S. West, Alga-fl. Yorks. 1900, p. 66; Alg. X. Ireland, 1902, p. 30. 



Didymidium (Micrasterias} denticulatum Reinsch, Algenfl. Frank. 1867, 

 p. 147. 



Micrasterias furcata Ag. var. denticulata Rabenh. Flor. Europ. Alg. Ill, 

 1868, p. 192. 



Helierella denticulata Eomtze, Revis. gen. plant. 1891, p. 898. 



Cells large, about 1-g times longer than broad, 

 broadly elliptic in outline, deeply constricted, sinus 

 narrowly linear ; semicells 5-lobed, interlobular in- 

 cisions narrowly linear ; polar lobe narrowly cuneate, 

 with dilated apex and concave sides, not projecting 

 beyond the lateral lobes, apical margin retuse with a 

 widely-open notch in the centre, angles obtuse or 

 sometimes truncate emarginate ; lateral lobes almost 

 equal and broadly cuneate, superior lateral lobes some- 

 times a little larger than inferior ones, divided into 

 two lobules by a deep incision, each lobule further 

 divided into four (sometimes only two) subequal, retuse 

 or emarginate parts. Side view of semicell narrowly 

 pyramidate, with a marked protuberance on each side 

 near the base. Vertical view fusiform, poles acutely 

 conical, with three undulations at the middle on each 

 side. Cell-wall delicately or sometimes coarsely 

 punctate. 



Zygospore globose, furnished with scattered, elon- 

 gate, stout spines with bifid and trifid apices, some of 

 which sometimes divide again and become recurved. 



Length 205-350 /* ; breadth 1 77-277 /u; breadth of 



