vv. 



SYSTEMATIC HISTORY OF THE INFUSO-RIA, 



destruction of the colouring matter, and at each end are two, more or less 



distinct, pellucid puncta In Grammonema there is scarcely any sihca, 



and the filaments are not fragile, but highly mucous, adhering firmly to paper 

 or glass, and when dried appearing hke a mere stain ; the application of nitric 

 acid or of a red heat destroys their form, and I can perceive no pimcta at the 

 ends of the frustules." Ralfs, Ehrenberg, and Kiitzing place this genus with 

 the Desmidieae because of the absence of silica ; and Meneghini says, " I think 

 this conclusion right. It is a true Desmidiean, for it has no silicious shield ; 

 and it is to be observed that, however perfectly it may resemble the Fragi- 

 larieae in form, it wants the longitudinal canals and terminal perforations of 

 the primary surfaces." 



Grammonema Jurgensn (Ag.). — 

 Valves oblong lanceolate, slightly con- 

 stricted at the obtuse ends. Ag CD. 

 p. 63. =Fragilaria Jurf/ensii, KSD. p. 59 ; 

 Cottferva striatida, Jurg. ; Fragilaria 

 striatula, Lyngb Hyd Dan. p. 183, t. 63 ; 

 SBD. ii. pi. 23. f. 298; Grammatonema 

 stnatidum, KSA. p. 187; Arthrodesmus 

 striatulus, ERBA. 1840; Frmjdaria au- 



rea, Cserm. in Hook B Fl. ii. p. 403. 

 /3. diatomoides, filaments tm'uing greenish 

 when dried, = Fragilaria diatomoides, 

 Grev., Hook B Fl. p. 403. On marine 

 Alg?e. Spring, Europe, (xv. 24, 25.) 

 Grammonema Jurgensii is easily distin- 

 guished from every species of Fragilaria 

 by its marine habitat and flexible, highly 

 mucous filaments. 



Genus DIATOMA (Dec). — Frustules quadi^angular, partially separating, 

 and cohering by the angles (generally by the alternate ones) into a zigzag 

 chain. Diatoma is distinguished from Fragilaria and Odontidiimi by the con- 

 nexion of the frustules at their angles in a zigzag chain. Some species of 

 Fragilaria, indeed, have a few frustules similarly adhering ; but this is a con- 

 stant character in Diatoma, whilst the greater number of their frustules will 

 present the usual appearance of a Fragilaria. Meneghini says, " For my part, 

 I think it would be much m.ore natural to place the smooth species {D. pec- 

 tinale, D. vitreum, and Z>. hiiaJinum) in Fragilaria ; those striated with elliptic- 

 lanceolate surfaces {D. vulgare, D. mesodon, D. tenue, and B. mesolej^tum) in 

 Odontidium. There would remain as distinctly generic the species which 

 have capitate extremities on their lateral surfaces. These unions woidd be 

 justified on both sides ; for whilst the Odontidia have forms little different 

 from Diatoma, Diatomata are httle difi'erent from Fragilaria." 



* StricB obsolete. 



Diatoma hyalinmn (K.). — Frustules 

 elongated, very hyaline; valves linear 

 lanceolate, with rather obtuse apices ; 

 striae obsolete. KB. p. 47, t. 17. f. 20 ; 

 SBD. ii. pi. 41. f 312. Marine. Europe. 

 (IV. 16.) 



D. minimum (Ealfs). — Frustides mi- 

 nute, very hyaline; valves about twice 

 as long as broad, oblong with rounded 

 ends ; striae obsolete. Ralfs, T Bot Soc. 

 2nd ed. p. 20 ; SBD. ii. p. 41, pi. 41. f 313. 

 = Z).rjYre?««, KB. p.47. Marine. Europe. 



D. pectinale (Nitz., K.). — Frustides at 

 first forming a fascia, afterwards zigzag ; 

 valves acutely lanceolate ; striae obsolete. 

 KB. p. 47, t.'l7. f 11. = Bacillaria pecti- 

 7mlis, Nitz ; B. seriata, Ptolemai, Jioceu- 

 losa, E Inf. Fresh water. Egypt, Eu- 

 rope, England. 



2 * Strioi (costce) evident. 



D. rid gar e (Bory)c — Valves spindle- 

 shaped, suddenly contracted at the ob- 

 tuse ends ; costae pervious, conspicuous, 

 about 18 in 001". KB. t. 17. f 15; SBD. 

 p. 39, pi. 40. f. 309 ; Bacillaria vulgaris, 

 E Inf. p. 197 ; Diatoma tenue, Grev., 

 HBFl. p. 406; D. Jloccidosum, A^CVf. 

 p. 53. Europe, Asia, Africa, and Ame- 

 rica. Frustules three or four times as long 

 as broad. This species is distinguished 

 by the greater breadth and convexity of 

 its frustides, and by the conspicuous 

 marginal puncta of the front view, 

 (iv. 13 ; IX. 168.) 



D. mesodon (K.). — Valves ventricose 

 lanceolate, with three to five transverse 

 stria? at the middle. KB. p. 47, 1. 17. 

 f 13. (:i. euneatum, frustides cuneate. 

 KB. t. 17. f 12, = Bacillaria cuneata, E 



