728 The American Naturalist. [August, 
States.*—This work of Mr. Stokes has been prepared with special 
reference to the needs of beginners in the study of Algs and Desmids, 
for whom the author believes analytical keys are absolutely essential. 
Generally speaking an artificial one is more useful than a natural one 
which involves more or less dissection, ruinous to the specimen, and a 
knowledge of characters that a beginner does not possess. 
The keys offered by Mr. Stokes are founded on the classification in . 
Wolles Monographs on the fresh water Algs and Desmids of this 
country, and references to these works are given for extended descrip- 
tions of the species. 
Directions for the collection, preservation and mounting of these 
microscopic plants are given, with a list of the best preserving media 
in the order of their excellence. 
The plate illustrating the genera of Desmids is a valuable adjunct 
to the work. 
Gasteropoda and Cephalopoda of the New Jersey Creta- 
ceous Marls.’—This volume, in reality a Monograph of the subject, has 
been prepared by Professor Robert P. Whitfield for the Geological 
Survey of New Jersey. It constitutes the second volume of a series 
which is intended to include descriptions of all the fossil invertebrates 
found in the New Jersey Cretaceous Marls. The following is a synop- 
sis of the Classified List which accompanies the work : 
INV OF THE NEW JERSEY CRETACEOUS MARLS. 
Gasteropoda. 
Genera Species 
Subelass Prosobranchiata 
Order Pectinibranchiata 54 119 
Order Scutibranchiata 5 6 
Subelass Opisthobranchiata : 
Order Tectibranchiata 6 6 
Scaphoda. 
Family Dentalium 8 4 
* Analytical Keys to the Genera and Species of the Fresh Water Algæ 
and the Desmidiez of the United States. By Alfred Stokes. Portland, 
Conn., 1893. " 
 * Gasteropoda and Cephalopoda of the Raritan Clays and Greensand 
_ Maris of New Jersey. By Robert P. Whitfield. Trenton, 1892. 
