STATE GEOLOGIST. ' 93- 



The authors who have done the most to elucidate this genus are 

 Schoedler, P. E. Mueller, and Kurz. Birge has corftributed most 

 largely, thus far, to the knowledge of American species, which are, 

 for the most part, identical or very close to the European. No 

 other genus is so difficult among the Lynceidse, for the most minute 

 differences are relied upon to distinguish species. The species of" 

 this genus are not greatly altered by the production of the winter 

 eggs. The males are frequently but little smaller than the opposite 

 sex, and are recognized by the altered form of the post-abdomen^ 

 and the presence of a hook on the first foot. The form is more 

 perfectly rectangular than in the next section; the shell is only 

 exceptionally reticulated and very rarely tuberculate, occasionally 

 smooth. The lower angle of the shell is not armed with spines, 

 but is generally rounded. There is only one basal spine upon the 

 claw of the post-abdomen, which usually bears a row of scales beside 

 the anal spines. The antenna have eight setae. The claw of the 

 male post- abdomen is removed from the lower angle. 



About twenty species are known, all of which that seemed recog- 

 nizably defined have been included in the following key, which is 

 believed to be more nearly natural in its arrangement than that of 

 Kurz, which would separate the European and American represen- 

 tatives of the A. parvula group. Many more forms remain to re- 

 ward the labor of American students. Those mentioned from^ 

 Minnesota could probably all be found by a few days search in one- 

 locality. 



Kky TO Section A, Alona. 



A. Shell reticulate. 



(a) Reticulations horizontal. 



1. A. guttata, Sars. 



(b) Reticulations oblique. 



2. A. angutata, Birge. 



B. Shell lined, smooth or tuberculate. 

 (a) Over 0.5 mm. in length. 



I. Shell densely striate. 



3. A. sanrjuinea, P. E. Mueller. 



II. Shell normally, evidently striate. 

 * Post-abdomen narrowed at the end. 



+ Armed with elongate teeth below. 



4. A. tenuicaudis, Sars. 



tt Teeth of post-abdomen nearly equal. 



5. A. lineata. Fischer. (Shell arched.) 



