296 GEOLOGICAL SURVEY OF THE TERRITORIES. 
Prof. A. E. Verrill, Mr. Edward Burgess, Dr. E. Coues; acknowledg- 
ments of whose valuable aid are made in their appropnate places. 
In the following pages I have touched upon some points in the inter- 
nal anatomy of these interesting Crustacea, and only regret that want 
of time has prevented me from entering more into detail. For a num- 
ber of microscopic slides of Branchipus, Thamnocephalus, Estheria, 
&e., 1 am much indebted to the friendly aid and skillof Norman N. 
Mason, esq., of Providence, R. I. . 
I desire also to express my thanks to Prof. F. V. Hayden, for the kind 
interest which he has taken in this work, and for the liberal number of 
plates with which the essay has been illustrated. 
The chapter on the development of the young of Apus lucasanus and 
Streptocephalus texanus has been contributed by Dr. C. F. Gissler, of 
Brooklyn, N. Y., who made the drawings which illustrate the text, and 
also those composing Plates XXXIV and XXXV. A number of the 
drawings of the entire animal of the species of Apus and Lepidurus, 
&ec., were made by Mr. J. H. Emerton; some anatomical drawings in 
the plates were prepared by Mr. J.S. Kingley, while I am under obliga- 
tions to Mr. Edward Burgess for the masterly manner in which he has 
executed the difficult sketches of the animals of Limnetis brevifrons, 
Estheria of several species, Hulimnadia, and Branchipus vernalis. 
I. CLASSIFICATION OF THE LIVING PHYLLOPODA. 
HISTORY OF THE SUBORDER PHYLLOPODA. 
The history of this group is an interesting one. Originally mentioned 
in 1785, by O. F. Miiller, in his ‘““Hntomostraca seu Insecta testacea,” the 
Entomostraca were first defined in 1806, by Latreille, in his Genera Crus- 
taceorum, &e. Under Legio prima, Entomostraca, the Phyllopoda con- 
stituted the third order, the sole representative of this order being 
Apus, while the genus Branchiopoda (Branchipus of Schoeffer) forms 
part of a sixth order, Cephalota. The other genera of Phyllopods were 
not then known. 
In 1820, Brongniart proposed the genus Limnadia for Hermann’s 
Daphnia gigas (1804). 
Meanwhile in 1817, in the first edition of Cuvier’s Régne Animal, the 
order Branchiopoda was proposed by Latreille, while the classification of 
this order was further amended and improved in the second edition of 
this work (1829). In this edition the Phyllopoda constitute the second 
suborder of the Branchiopoda, and now the Phyllopods comprise the 
genera Limnadia, Branchipus, Artemia, and Apus. 
In 1837, Straus-Durckheim described the genus Estheria, of which 
Cyzicus of Audouin (1837) and Isaura Joly (1842) are synonyms. The 
genus Limnetis was described by Lovén in 1845. 
In 1840, Milne-Edwards, in his Histoire Naturelle des Crustaces, es- 
tablished the Legion Branchiopodes, equivalent to the Entomostraces. 
Under the Branchiopoda he regards the Phyllopoda as forming an order, 
and they are succeeded by the Cladocera, while the Legion of Entomo- 
straca comprises the Ostracoda and Copepoda. 
In 1853, Prof. J. D. Dana, in the Crustacea of the United States Ex- 
ploring Expedition, regarded the Phyllopoda as constituting the second 
Legion of his first order (Gnathostomata) of Entomostraca. 
In 1863, Gerstaecker regarded the Phyllopoda as forming a family of 
the order Branchiopoda, the Trilobita, Cladocera, and Ostracoda, forming 
the remaining families. Claus, in 1868 (Grundziige der Zoologie), divided 
