“Oe, NOTES AND COMMENTS. 9 
bivalved mollusca; and he publishes the following scheme in the 
Zoologischer Anzeigey for October 24 (vol xv., pp. 373—375) aS most in 
accordance with the existing state of knowledge :— 
Class: LAMELLIBRANCHIATA (PELECYPODA). 
Sub-Class I: PRoToBRANCHIATA.—With double comb-shaped 
gills; hinge toothless or with interlocking denticulations of 
the hinge-border or taxodont. Families: Vlastidz, Cardio- 
lida, Antipleuride, Lunulicardiide, Preecardiide, Silurinide, 
Protomyide [Solenomya], Solenopside, Grammysiidz, Posi- 
donomyide, Daonellide, Nuculide. 
Sub-Class II. : DEsMopontTa.—With double lamellar gills ; hinge- 
teeth wanting or irregular, arising in intimate connection 
with the ligament supports. Families: Pholadomyide, 
Myide, Anatinide, Panopzide, Septibranchia, Mactride, 
Pholadid#, Gastrochenide. 
Sub-Class III.—Amponoponta. With double lamellar gills; 
hinge-teeth inclined backwards on the hinge-plate of the 
shell, variable in position, may be wanting. 
Order 1. Eutaxodonta. With taxodont hinge. Family : 
Arcide. 
Order 2. WHetevodonta. With heterodont hinge. Families: 
Astartide, Crassatellide, Chamide, Lucinide, Cardiide, 
Tridacnide, Cyrenide, Cyprinidae, Veneride, Solenide, 
Tellinide, Donacide. 
Order 3. Schizodonta. With schizodont hinge. Families: Tri- 
goniide, Najadz. 
Order 4. Anisomyaria. Hinge-teeth wanting, orif present, isodont 
or irregular; with two very dissimilar hinge-muscles or 
merely a single hinge-muscle. Families: Aviculide, Myti- 
lide, Pinnide, Pectinide, Spondylide, Ostreide, Anomiide. 
THE CURVATURE OF PLANTs. 
Mr. Francis Darwin and Miss D. Pertz have lately been 
studying the artificial production of rhythm in plants, and the 
results appear in the last number of the Aunals of Botany. The obser- 
vations were made with the help of a new machine devised by the 
authors, which they call an intermittent klinostat. It differs from the 
ordinary klinostat in that movement is allowed only at regular 
intervals. The spindle is connected with a clock in such a way that 
a half rotation, 7.c., of 180 degrees, occurs at the end of every half- 
hour. Experiments were made with relation both to geotropic and 
heliotropic curvatures. In the former series, shoots of valerian and 
stalks of dandelion were used; these were fixed through a bored cork 
in test-tubes of water, which were attached horizontally to the 
spindle. The machine was placed opposite a window to cancel the 
effect of light in causing curvatures. When the clock was working, 
the influence of gravity on the growing shoot or stalk was, of course, 
reversed every half-hour, and it therefore received a stimulus of equal 
duration to curve towards opposite sides. 
After the first few half-hourly intervals, the curvatures in either 
direction continued regularly for about thirty minutes. If the clock 
