PALMELLACE, 19 
Genus 13. RHAPHIDIUM. Kutz. (1845.) 
Cells fusiform, or cylindrical, generally very gradually cuspi- 
date or acuminate at the ends, rarely obtuse, straight or 
variously curved, single, geminate, or fasciculately aggregate, 
decussate in the centre, or radiately conjoined, rarely two 
laterally united at the end, other cells free. Tegument thin, 
smooth. Contents green, very finely granular, furnished with a 
central, or rarely lateral, transparent vacuole. Division of the 
cells only in one direction. 
Rhaphidium aciculare. Braun. Rabh. Exs. 442. 
Very slender, 15-20 times as long as broad, yellow-green, 
often single, acicular, acutely cuspidate at each end, straight, or 
slightly curved or somewhat lunate. 
Ankistrodesmus acutissimus, Archer in Micr. Journ., 1862, t. 
xii. f. 44-56. ‘ 
Closterium Griffithii, Berk. Ann. Nat, Hist. xiii. 256, t. 14, 
f, 2. 
Rhaphidium polymorphum var. y aciculare, Rabh. Alg. iii. 45. 
In pools, 
“Cells very minute, 20-25 times longer than broad, fusiform, very 
slender, straight, very acutely acicular, solitary or forming fasciculi of 
2-4 cells ; endochrome light-green, mostly with a minute parietal semi- 
circular or rounded pale body or space placed near the middle of the 
cell, otherwise usually appearing homogenous, sometimes slightly 
granular.” It agrees with #. falcatum in its very slender and acute 
cells, but it differs from it by its straight, not arcuate cells, by its fusi- 
form more quickly attenuated cells, by its more intensely acute extremi- 
ties, and by the constituent cells of an old fasciculus being much fewer 
in number.— Archer. 
Plate VIII. fiy. 3. Cells magnified 400 diam. 
Rhaphidium falcatum. (Corda.) 
Fusiform, slender, acutely cuspidate at each extremity, 
curved, or semi-lunar, 4-16 congregated in fascicles. 
Micrasterias falcata, Corda Alm. Carls, 1835, p. 121, t. 2, 
f, 29. 
Staurastrum falcatum, Ehr. Weigm. Arch. 1836, p. 185. 
Closterium falcatum, Meneg. Linnea, 1840, p. 233. 
Ankistrodesmus gregarius, Breb. in litt. 
Ankistrodesmus falcatus, Ralfs Desm. t. 34, f. 3. 
Rhaphidium polymorphum, var. c. faleatum, Rabh. Alg. iii, 45. 
In pools. 
It is a very common plant in ponds, &c.,and resembles a minute 
young Closterrum, except that although some individuals may be soli- 
tary, others will be seen in the same gathering collected in the charac- 
teristic fascicles. 
Plate VIII. fig. 4. a, families magnified 400 ; 6, magnified 800 diam. 
