AETHKODKSML'S. 109 



When in the plankton the spines of A. convergent JM-O 

 frequently much reduced. 



The form recorded as " forma membrana irregulariter 

 punctatV (cf. W. & G. S. West, 'New Brit, Freshw. Alg.' 

 1894, p. 9) cannot be regarded as a distinct form,, as many 

 specimens of this species clearly show a finely punctate 

 cell- wall. 



In a variety of this species (var. incrassatus Gutw.) which 

 occurs in Austria and in the United States the cell-wall is 

 thickened by two transverse bars of cellulose stretching 

 across the semicell on each side of the apex. 



9. Arthrodesmus subulatus Kiitz. 

 (PI. CXVI, fig. 14; PI. CXVIT, fig. 1.) 



Arthrodesmus subulatus Kiitz. Spec. Alg. 1849, p. 176; Nordst. Desin. 



Brasil. 1870, p. 232, t. 4. f. 59 [forma major] ; Wolle, Desm. U. S. 1884, 



p. 96, t. 24, f. 11, 12 ; De Toni," Syll. Alg. 1889, p. 1059 ; Borges. Desin. 



Brasil. 1890, p. 43, t. 5, f. 57 [forma major] ; Turn. Freshw. Alg. E. 



India, 1893, p. 133 [forma media and forma minor] ; Rov & Biss. Scott. 



Desm. 1894, p. 41 ; West, Alg. Madag. 1895, p. 72, t. 9, f. 32, 33 ; Some 



N. Anier. Desm. 1896, p. 254 ; Borge, Alg. erst. Eegnell. Exped. II. 



Desmid. 1903, p. 103 ; W. & G. S. West, Scott. Freshw. Plankton, I, 



1903, p. 528. 

 A. convergens Ehrenb. var. subulatus (Kiitz.) Kabenh. Flor. Europ. Alg. 



Ill, 1868, p. 227. 



Cells of medium size, about as long as broad (without 

 the spines), deeply constricted, sinus widely open from 

 a more or less subacunimate apex ; semicells elliptic - 

 obsemicircular, ventral margin much more convex 

 than the dorsal margin (almost semicircular), lateral 

 angles somewhat rounded, each furnished with a long, 

 stout, straight, and horizontally disposed spine. 

 Vertical view elliptic, each pole furnished with a long 

 straight spine. Cell-wall finely punctate. 



Zygospore globose and smooth. 



Length 28*4-50 (JL ; breadth without spines 27-54 p., 

 with spines 52-100 //, ; breadth of isthmus 7-13'5/u; 

 thickness 15-22 /A; diam. zygosp. 30-36 p.. 



SCOTLAND. Slewdrum, Cambus O'Mav, and Glen 



. ^ ' 



Clunie, Aberdeen (Roy fy Bissett). 



IRELAND.- -Dublin and AYicklow (Archer). 



Geocjr. Distribution. --India. Madagascar. Abys- 

 sinia. United States. Brazil. Paraguay. 



