PALMELLACE^E. 19 



GENUS 13. RHAPHZDIUftl. 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 acutissinius, 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 ; endochronae 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 R. 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 VIIL Jig. 3. Cells magnified 400 diam. 



Rhaphidium falcatum. (Cor da.) 



Fusiform, slender, acutely cuspidate at each extremity, 

 curved, or semi-lunar, 4-16 congregated in fascicles. 



Micrasterias falcata, Corda Aim. Carls. 1835, p. 121, t. 2, 



f. 29. 



Staurastrum falcatum, Ehr. Weigm. Arch. 1836, p. 185. 

 Closterium falcatum, Meneg. Linnaaa, 1840, p. 233. 

 Ankistrodesmus gregarius, Breb. in litt. 

 Ankistrodesmus falcatas, Ralfs Desm. t. 34, f. 3. 

 Rhaphidium poly morp hum, var. c. falcatum, Rabh. Alg. iii, 45. 



In pools. 



It is a very common plant in ponds, &c., and resembles a minute 

 young Closterium, except that although some individuals may be soli- 

 tary, others will be seen in the same gathering collected in the charac- 

 teristic fascicles. 



Plate VIIL Jig. 4. a, families magnified 400 ; b, magnified 800 diam. 



