34 COCCOPHYCES. 
var. c. G@imorphus. Rabh. Alg. 111., 63. 
Cells acute, 4-8, placed evenly in a single row; inner cells 
fusiform, outer externally lunate. 
Scenedesmus dimorphus, Ralfs. Ann. Nat. Hist xv., p. 403, 
t.12,f.5. Brit. Desm. p. 191, t. 381, f.13. Hass. Alg. 393, 
t.92, f. 13. 
Formerly the typical form and its two varieties were regarded as three 
separate species, but there scarcely seems sufficient reason for thus re- 
taining them. Ralfs wrote of them long ago, ‘‘ When the cells are nearly 
uniform S. acutus has some resemblance to S. dimorphus; but in the 
latter the cells are more slender, never ventricose, and are arranged 
quite evenly side by side. It is more difficult to distinguish S. acutus 
from S. obliquus, and Iam far from certain that Ehrenberg erred in 
uniting them. The principal distinction is that in 8. acutus the cells 
form only a single series, which is nevertheless irregular, on account of 
the alternate projection of the cells in opposite directions. In 8. obliquus, 
on the other hand, the cells by division form two distinct rows, which, 
after separation, become two fronds.” These characteristics are better 
shown in Ralfs’ figures than in our own, which are more intermediate, 
and show an evident approximation to the typical form. 
Plate XITI. fig. 6. a, cells of the typical form ; 8, cells of the variety 
- dimorphus; c, of the variety odliguus. All magnified 400 diameters. 
Scenedesmus antennatus. Breb. Ralf. Desm. t. 35, f. 27. 
Cells fusiform, 2-4-8, joined in a single or double series, all 
somewhat curved, usually ventricose, cuspidate at each extremity, 
the apices bearing a hyaline globule. 
Size. Cells -0025--0035 mm. diam., ‘013 mm. long. 
Rabh. Alg. iii. 68. Archer in Pritch. Infus. p. 753. 
In pools. 
“ Scenedesmus antennatus resembles S. acutus in form, and also in the 
arrangements of the cells; but is distinguished from that and every 
other species by having the attenuated points tipped by minute glo- 
bules.”—Raljs. 
At the time the above was written it had not been found in this 
country, and is still the rarest species, if its specific identity can be 
maintained. 
Plate XIII. fig. 7. Cells magnified 400 diameters. 
B. Cells armed. 
Scenedesmus quadricauda. Breb. Ralfs Desm. 190, t. 31, f. 12. 
Cells oblong-cylindrical, each extremity obtusely rounded, 
2-4-8, narrowly united, either in a single or double series, all 
straight, the outer cells at each end (and rarely some of the 
intermediate ones) armed at each extremity with a recurved 
spine. 
ies Cells :0085-:01 mm: diam. to ‘022 mm. long. 
Rabh. Alg. iii. 65. 
Scenedesmus quadricaudatus, Ralfs Ann, Nat. Hist. xv., p. 
402, t.12,f.4. Hass. Alg. 392, t.92,f.12. Jenner Fl. Tun. 
Wells, p. 200. 
In standing water. 
