REVIEWS. 
481 
Geographical Survey of the United States Territories."” 
At the same time^ the authorities can only be congratulated 
on the wise liberality which has led them to undertake the 
production of so valuable a work. We have here figured 
and described by Dr. Leidy, in the most ample manner, a 
large series of those freshwater forms which Mr. Archer, of 
Dublin, was the first to detect, and to study in a special 
manner. Focke, Franz Schulze, Lesser, Hertwig, and Dr. 
Leidy, have added to and expanded the rich store, which 
was first tapped and offered to the zoological connoisseur in 
the pages of this Journal. To the old and well-known 
genera of freshwater E-hizopods — Amoeba, Gromia, Arcella, 
Difflugia, Actinophrys — a host of remarkable allies have 
now been added. In the present fine monograph Dr. Leidy 
describes many already known genera and species which he 
has detected on the North American continent, but he also 
describes several new and very interesting forms, e,g. Din- 
amoeba, Ouramoeba, and Biomyxa. The volume is illustrated 
by forty-eight quarto plates, and must be carefully studied 
by every student of Rhizopod faunae. We should have been 
glad had it come into the plan of Dr. Leidy^s studies to 
devote more attention to the determination of minute 
structure as revealed by powers higher than one of 250 
diameters. 
A History of the British Marine Polyzoa. By Thomas 
Hincks, B.A., F.R.S. Van Voorst, London. 
The well-known and highly valued series of works on 
Natural History, published by Mr. Van Voorst, is worthily 
extended by the two admirable volumes, one of text, one of 
plates, treating of the British Polyzoa, by the Rev. T. 
Hincks. In an introduction of a hundred and forty pages, 
illustrated with numerous cuts, the comparative anatomy 
and general morphology of the Polyzoa are very fully and 
clearly discussed — the most recent investigations — French, 
German, and Swedish, all receiving due notice. In the 
systematic part which follows the groups of Polyzoa are 
taken up one by one and systematically characterised, until 
the whole hierarchy, down to families, genera, species, and 
varieties, is exhausted. The characteristics of species, as 
well as of genera, and even of suborders, are necessarily 
chiefly, if not entirely, drawn from the structure of the hard 
parts. These are very extensively and beautifully figured' 
in the atlas, so that by the aid of this work the student of 
