Protococcacece 



223 



apices of the former, and I do not regard this as a sufficient 

 generic difference. " Reinschiella ? setigera" must be considered 

 as an Ankistrodesmus having the same relationship to other 

 species of the genus as Dactylococcus bicaudatus has to other 

 species of Dactylococcus. 



Fig. 94. A, Ankistrodesmus falcatus (Corda) Ealfs, from Bowness, Westmoreland. 

 B and C, A. falcatus var. acicularis (A. Br.); B, from Pilmoor, N. Yorks. ; 

 C, from the plankton of Loch M. Bharabhais, Lewis, Outer Hebrides. D, A. 

 falcatus var. tumidus nob., from Puttenham Common, Surrey. E, A. falcatus 

 var. mirabilis nob., from Wimbledon Common, Surrey. F, A. setigerus (Schrb'd.) 

 nob., from near Kievaulx Abbey, N. Yorks. G and H, A. Pfitzeri (Schrod.) nob., 

 from the plankton of Loch M. Bharabhais, Lewis. (All x 520.) auts, autospores. 



As plants of this genus are often very abundant and the synonymy is 

 much confused, the following synopsis will be found useful : 



A. falcatus (Corda) Ralfs. [Micrasterias falcata Corda 1835 ; Ankistro- 

 desmus fusiformis Corda 1 838 (in part) ; Rhaphidium fasciculatum Kiitz. 

 1845 ; Rh. potymorphum Fresen. var. falcatum Rabenh.] Cells lunate or 

 arcuate, 16 24 times longer than the diameter (1'5 3 p.), with the apices 

 acute ; associated in loose aggregates or close bundles, rarely solitary. 

 Chloroplast usually devoid of a pyrenoid. Fig. 94 A. 



Var. acicularis . [Rhaphidium aciculare A. Br. 1849 ; Rh. polymorphum 

 var. aciculare Rabenh. ; Closterium subtile Breb. ; Ankistrodesmus acutissimus 

 Arch. 1862.] Cells usually solitary, commonly straight or slightly curved, 

 with acutely attenuated apices. Length 36 65 p. ; breadth 2 -5 3'5 /x. 

 Chloroplast sometimes furnished with one pyreiioid (or more). Fig. 94 B 

 and C. It is most probable that Rh. pyrogenum Chod. belongs here. 



Var. duplex . [Rhaphidium duplex Kiitz. 1845.] Cells elongate, sig- 

 moid, associated end to end in pairs. Rh. nivale Chod. may possibly be a 

 form of this variety. 



