338 THE AMERICAN- NATURALIST.: (VoL. XXXIII. 
the anatomical descriptions are in some cases omitted or incomplete, 
that the keys were not in all cases revised to meet the new classifica- 
tion, and that the limits of Mr. Simpson’s contributions were not 
more definitely marked. We also note that A/ax, the common 
Hydrachnid parasite of the clam, is incorrectly reported as Dip/o- 
dontus. The plates —half-tones from photographs of the shells — 
afford abundant illustrations, and are in some cases excellent, though 
they at times fail to reveal important details of structure, such as the 
beaks and the hinge teeth. The full descriptions, the abundant illus- 
trations, and the keys make the work a valuable handbook for Amer- 
ican collectors and students of fresh-water Pelecypoda. CG a x. 
Rotifera and Protozoa of the Illinois River. — The local and 
seasonal distribution of ninety-three Protozoa and one hundred and 
eight Rotifera is given by Mr. Hempel ‘as a result of his examination 
of towings made during 1894 and 1895 in the Illinois River and its 
adjacent waters. The results reported afford further data indicative 
of the cosmopolitan distribution of these groups, and the similarity 
of the pelagic fauna of the fresh water of Europe and America. Some 
species occur throughout the whole year, or a greater part of it, while 
others recur only at stated seasons; some reach a maximum in the 
spring, others in the summer, and still others in the fall, while some 
reach this condition only in the winter, breeding abundantly under 
the ice. The predominance of the Brachionidz among the Rotifera 
is noticeable. One new species, Diffiugia fragosa, is described. 
As tk. 
Diurnal Migration of the Plankton.?— A single series of observa- 
tions on the quantity of plankton at certain levels in Lake Leman, by 
Dr. H. Blanc, suggests a considerable vertical movement, especially 
of the Entomostraca, toward the surface during the night. Catches 
were made at the surface, and at depths of 20, 40, and 60 meters in 
water 100 meters deep. The volume of the catch from surface water 
at 4 A.M. was 25 times as great as it was at 4 P.M. A large increase 
also occurred in the catch at the 20-meter level, while at 40 and 60 
meters there was no considerable change. The afternoon catch at 
1 Hempel, A. A List of the Protozoa and Rotifera found in the Illinois River 
and Adjacent Lakes at Havana, Ill., Bull. ZI. State Lab. Nat. Hist., vol. v (1898), 
pp. 301-388. 
2 Blanc, H. Le Plankton nocturne du lac Leman, Bull. Soc. Vand. Sci. Nat. 
vol. xxxiv (1898), pp. 225-230, Pl. II. 
