4 THE JOURNAL OF BOTANY 



outward form, but on the whole they are somewhat irregularly 

 elliptical in their broadest aspect. The posterior extremity is in 

 many instances bluntly conical and the anterior extremity is con- 

 spicuously notched. The cell is much compressed and in its 

 narrow aspect it is linear-oblong, with a subtruncate and shghtly 

 notched anterior extremity and a rounded-conical, slightly curved 

 posterior extremity. This curvature of the tail in the narrow 

 aspect was a constant feature of all individuals. A careful 

 examination of the solid geometry of the cell shows that at the 

 anterior end there is a notable depression which is surrounded by 

 four mamillate projections (hence the specific name " tetrathele "), 

 and it is from the base of this depression that the cilia arise. The 

 four cilia are somewhat short, being only three-quarters the length 

 of the body of the organism. The chloroplast is large and occupies 

 most of the cell. It consists of four anterior lobes, each of which 

 extends from one of the front mamillate projections to a point just 

 behind the middle of the cell, where the lobes unite together. Four 

 other shorter lobes then extend posteriorly. iVt the point of union 

 of the lobes there is a large rounded pyrenoid, which is thus 

 situated behind the middle region of the ceh. There is a prominent 

 pigment-spot (or stigma) adjacent to the pyrenoid. The nucleus 

 is situated between the four anterior lobes of the chloroplast and 

 immediately in front of the pyrenoid. Two small contractile 

 vacuoles were present near the base of the cilia, but they could 

 only be observed with difficulty. 



The organism moves forwards with considerable rapidity and 

 revolves at the same time. It performs one complete revolution 

 in traversing a distance equal to three times its own length. 

 Sometimes it stops its forward progression and begins to spin 

 rapidly round " head over heels," so to speak ; that is, the plane 

 of revolution is longitudinal. This may be kept up for half a 

 a minute, and then forw^ard progression is renewed. 



As a rule two daughter-cells are formed by the longitudinal 

 division of the mother-cell. These face in opposite directions, and 

 are at first enclosed in the old w^all of the mother-cell. In very 

 rare instances four daughter-cells arise in one mother-cell. 



Platymonas belongs to the sub-family Carterieae of the 

 Volvocacese, and it is the second compressed genus of that sub- 

 family w^hich is now known. The other genus is Scherffelia 

 Pascher." Platymonas differs from Scherffelia in its less flattened 

 cells, in its subrectangular cross-section without any lateral wings, 

 in its four anterior mamillate projections, in its single lobed 

 chloroplast furnished with a large pyrenoid, and in the posterior 

 position of the stigma. Platymonas is also marine, whereas both 

 known species of Scherffelia are fresh-water organisms. 



XXI. — Some Further British Species of Chlamydomonas. 



1. Chlamydomonas brachyura, sp. nov. Cellulae vegetativse 

 ( = zoogonidia) late ellipsoidese cum polls leviter attenuatis, acutis 



* A. Pascher, " Zur Kenntnis zweier Volvokalen," Hedivigia, Hi, 1912. 



