No. 400.] REVIEWS OF RECENT LITERATURE. 331 
peculiarities. As compared with littoral species, those of deep water 
are more variable, being often irregular in shape or ornamentation, 
Quadrula, for example, lacking the regular arrangement of the plates 
of the shell. They are also of larger size, and are more transparent, 
being less heavily charged with salts of iron and manganese, which 
cause the brownish and purplish tints of the shell. The contractile 
vacuoles are less active, as they are in those species also which 
inhabit sea-water, and the capacity of encystment seems in large 
measure to, have been lost. Starch grains are frequently found in 
the protoplasm, though no Zoóchlorellae were detected. The author 
suggests that diatoms may be retained within the protoplasm for a 
considerable length of time undigested in a temporary symbiotic 
relationship. On account of the great similarity of the abyssal 
Rhizopoda of the different lakes not at present connected, the sep- 
arate origin of these faunas from the common littoral group is not 
accepted, and the idea is advanced that they represent a relict fauna 
of the preglacial or glacial period. C A. K. 
A New Colonial Flagellate. — The Illinois State Laboratory of 
Natural History has recently issued a bulletin! on 7/a£ydorina cau- 
data, an interesting new genus of the family Volvocidz, described 
by C. A. Kofoid. This is a colonial form of sixteen or thirty-two 
biflagellate cells arranged in a horseshoe-shaped coenobium which 
bears three or five tails, formed by the envelope at the posterior end. 
The cenobium is flattened, and is slightly twisted in a left spiral. 
The cells appear to be arranged in one layer, and the two faces of 
e plate are exactly alike, as alternate cells upon either face bear 
flagella. In development the young colonies pass through a Gonium 
and a Eudorina stage and subsequently flatten, so that the cells of the 
two faces are regularly intercalated. This genus presents the most 
pronounced type of functional and structural polarity, and exhibits a 
greater degree of axial differentiation than any other genus of the 
family. The organism has been found in late summer and fall 
months for four years past, and has occurred in the waters of the 
Upper Mississippi, Illinois, and Wabash basins. The paper contains 
a key to colonial Volvocidz. 
. 1 Kofoid, C. A. Plankton Studies. III. On Platydorina caudata, a new 
Genus of the Family Vólvocidz, from the Plankton of the Illinois River. Bul. ZU. 
State Lab. Nat. Hist., vol. v, pp. 419-440, Pl. XX XVIII, 1899. : 
