100 ' ANNUAL REPORT. 



Habitat. — " Grassy Lake," a pond tributary during high water to Lake Cal- 

 houn, near Minneapolis ; also Diamond Lake. The animal seems to be found in 

 lakes not completely isolated, and does not prefer so muddy a situation as most 

 of the Daphnioidea. 



The structure of this animal was compared minutely with the description given 

 by Dr. Baird of 5. Cr?/stoZZma, and is beyond doubt identical. Plates Viand VII. 



, FAMILY II. DAPHl^IDuE. 



Bibliography. — Daphnidse, Dana, Rep. Wilkes' Expl. Exp., p. 1265. 



Dana, Proc. Amer. Acad. Sci., ii., 1849. 



Daphnita, Gray, Cat. Brit. Crust. Brit. Mus., 88. 



Daphmadse, (part), Baird, Brit. Entomos. 62. 

 Characters. — Fohaceous feet ten. Anterior antennae one or two-jomted. 



1. Head large. 



Genus 1. Daphnia, Muller, (including Ceriodaphnia of Dana, which 



differ in the shape of the reticulations of the shell.) 

 Genus 2. Moina, Baird. 

 Genus 3. Macrothrix, i?airf? (including Acanthocerus of Schodler. ) 



2. Head short. 



Genus 4. Lynceus, Midler (including Eurycercus, Chydorus, Pera- 

 cantha, Pleuroxis, Acroperus, Campotercus and Alona of different 

 authors, until iome valid generic characters are announced.) 



Genus Daphnia, Muller. 



Bibliography. — Daphnia, Muller, Zool. Dan. Prod. 



Muller, Entomost. 



Straus, Desmarest, Latreille, etc. 



Monoculus, Linnoius, Poda, Blumenhach, De Geer, etc. 

 The Daphnise are among our most abundant and most interesting Entomostraca, 

 occurring in stagnant water everywhere, they are very prolific and voracious. 

 This genus is confined strictly to fresh water. 



The general characters will be gathered from the description of tlie tribe and 

 of the species. The superior antennae are usually rudimentary and hidden, but 

 vary with the sexes. The most prominent organs are the inferior antennae, 

 which are large and powerful. Tfiey consist at the base of a single large, fleshy 

 joint which has all possible play upon its attachments. This joint supports two 

 branches of nearly equal length, but the outer is usually four-jointed, while the 

 inner has but three articulations. Each of the last three is furnished with a 

 long seta which is jointed at the «niddie, and usually pecinate, forming a fine 

 swimming organ. The eye is a large, conspicuous organ near the front and is 

 so famished with muscles that it has a semi-rotation. This organ occupies a 

 prominence on the underside of the head, which projects backward supporting 

 the minute antennae and the black spot before noticed. Baird says that the eye 

 was naistaken by one author for the stomach. The chief ganglion of the nervous 

 system lies near and communicates with the eye. The mouth lies at the back of 

 tiie prominence described, and is armed with a labrum, a pair of mandibles and 

 a pair of Jaws. For particulars of structure see plate IX. 



