Notes on British Flagellates. I — IV. 347 
In many cases, however, they are only represented by isolated 
individuals, and are not very frequently met with in large numbers. 
Certain of the species of Cryptomonas appear to possess a very 
distinctive mode of progression. Speaking generally the unicellular 
motile type amongst the lower Algae is characterised by a rapid 
rotation on its own axis during the forward movement, and the same 
type of motion is exhibited by some of the species of Cryptomonas I 
have had under observation. Others, however, exhibit no rotation 
Fig. 2. Forms of Cryptomonas. A, form resembling C. nasuta. Pascher. 
B, C. compressa Pascher? C E, C. anomala n. sp., C and E viewed from the side, 
D from the dorsal surface; in C and D the chloroplasts are indicated by 
shading. F and G, C. ovata Ehrenb., forma. H, C. Richei n. sp. c, chloroplast; 
g, gullet; it, nucleus: p, pyrenoid. (A F x about 1400; G and H x about 
900). 
during their movements, the individual swaying gracefully first to 
one side and then to the other, during each of which swaying 
movements it performs a half-twist so as to expose now the one 
flank, now the other to the observer. This type of motion was 
particularly observed in two forms of Cryptomonas from the marsh 
at Keston, bearing a strong resemblance respectively to C. compressa 
Pascher (Fig. 2, B), and C. nasuta Pascher (Fig. 2, A). It seems 
probable that this method of progression is related to the dorsiven- 
trality of the Cryptomonad individual, but its occurrence in one 
