ALGOLOGICAL NOTES 3 



•genus of the family. The tank had been used for raising the 

 larvffi of a certain species of crab. Originally it contained the 

 crab ova, a number of stones to which were attached thalli of 

 Ulva Lactuca, and several gallons of sea-water. AW these came 

 from Plymouth, and it is highly probable that the two members 

 of the Volvocacese were present among the Ulva. The conditions 

 in the tank were evidently extraordinarily favourable for the rapid 

 increase of the two members of the Volvocaceae. 



The new genus is described as follow^s : 



Platymonas, gen. nov. Cellule vegetativse minut®, libere 

 natantes et motiles, vcdde compressm ; a fronte visas eUipticee vel 

 subellipticiE, polo anteriori cum incisura aperta minuta et cilios 

 quattuor hrevihus praedito, polo posteriori rotundato vel acute 

 rotundato ; a latere visas subanguste oblongs, polo anteriori sub- 

 truncato cum incisura minuta, polo posteriori leviter curvato et 

 rotundato-conico ; a vertice visce subrectangulares, angulis rotun- 

 datis et lateribus levissime concavis. Chromatophora singula, 

 viride, cum lobis elongatis anterioribus 4 et lobis brevibus posteri- 

 oribus 4, pyrenoide singulo partem posteriorern versus disposito ; 

 nucleo singulo mediano ; stigma conspicua posteriori pyrenoidem 

 proxima. Partitione prima cellulse matricalis Tongitudinali. 



P. tetrathele, sp. unica. (Fig. 1.) 



Long. cell. 14-16 p. ; lat. cell. 7'0-8 fx ; cross. 4-2-5 ft ; long, 

 ciliorum 9*5-12 /u. 



Hah. In a tank of sea-water, which had been received from 

 Plymouth, along with stones to which were attached fronds of 

 Ulva Lactuca. 



This organism is apparently a distinctive type of the sub- 

 family Carteriae of the Volvocaceae. The cells vary a little in 



G ^H 



Fig. I.— Platymonas tetrathele. A and B, broad aspect (front view) of the 

 •organism showing nucleus, pyrenoid, stigma and contractile vacuoles; C and D, 

 side views; E, oblique view; F and G, views of the organism seen from the 

 .anterior end (cilia not shown) ; H and I, division of cell to form two daughter- 

 cells ; J, four daughter-cells formed within the mother-cell. All x 1000. 



