18 TWELFTH ANNUAL REPORT. 



which to build. A few notes were published by the writer a little 

 later. 



A few additional notes and descriptions of new species were 

 published in the eleventh annual report of the Minnesota geol. 

 and nat. hist, surveij. 



Prof. Birge published other notes in the Medical Journal and 

 Examiner of Chicago, which I have not seen. 



Prof. Forbes of Normal, 111., in an article in the American 

 Naturalist, July, 1882, adds a number of facts and one new species. 



In addition to the above, a figure of Sida was printed in one 

 of Hayden's Survey Reports, and some account of the Cladocera 

 of lake Michigan was given by B, W. Thomas, I believe, in one of 

 the official reports of the Chicago Water Commission. 



CLASSIFICATION OF THE CLADOCERA. 



SUB-ORDER I.— CALYPTOMERA (membrane-clothed). 



Body enclosed in a bivalve shell. Mandibles truncate below. Maxillse distinct, 

 spiny. Tlioracic ganglia discrete. 



Tribe I. — Ctenopoda. 



Feet six, similar, foliaceous, all distinctly brancbiate. 

 FaM. 1. — SiDIDE. 



Swimming anteunfe with two unequal rami, intestine simple. 

 Fam. 2. — HOLOPEDID^. 



Swimming antennae simple, elongate cylindrical (in the male prehensile), 

 intestine with two lateral dilations. 



Tribe II. — Anomopoda. 



Feet five (or six) pairs, the anterior pair more or less prehensile and destitute 

 of branchise. 



Eam. 1. — Daphnid^. 



Rami of antennae three and four-jointed, five pairs of feet, the last with 

 a curved appendage guarding branchial sac; autennules of female 

 short, one-jointed. 



FaM. 2. — BOSMINID^. 



Six pairs of feet, antennules elongated, many-jointed. 



Fam. 3. — Lyncodaphnid^. 



Antennules of female elongated, but one-jointed; intestine simple or 

 convolute. 



Fam. 4. — Lynceid^e. 



Antennae with both rami three-jointed, intestine convolute, with ab- 

 dominal but no anterior caeca. 



SUB-ORDER II.— GYMNOMERA (destitute of covering). 



Body without or nearly destitute of bivalve shell ; feet not branchiate, spiny. An- 

 terior thoracic ganglia in one mass. 



