132 rKOCKEDINGS OF THE ACADEMY OF [Jan. 



— in three species of DUparoneura, in three of Neoneura and in 

 three of Protoneura — the same variation is seen, from the poste- 

 rior end of the sixth to the anterior of the seventh; of the Legion 

 Agrion it appears in the sixth segment in Hyponeura liigens, 

 Ischnura heterodieta, Eiiallarjma ebrium, geminatum and asper- 

 sum, m Nehalentiia lal-<, Ceriagrion glahrum, Anlmgrion aUoptenim 

 and JSemiphlebia mlrahiUs ; in the fifth in Argia jmtrida, Pyv' 

 rhosoma tenellum; in the seventh in LepUAgrion macrurum and Lep- 

 tohaais vacillam ; of the legion Le-ite-i it appears in the sixth 

 segment in Lestes disjiuida and L. leda. 



Armature of the Adult Gizzard. 



To save the necessity of giving lengthy descriptions of the 

 arraatui'e of each gizzard studied, and more especially to render 

 the comparison of tliese armatures more easy, it was found con- 

 venient to construct a formula whereby the general structure of 

 the armature might be indicated. 



Below is given an explanation of the formulie used: 



F, F, f, indicate specially chitinized areas of the gizzard lining, 

 whether they bear teeth or not. They may stand as abbrevia- 

 tions of "field" ("Felder" of Ris) or '''fold." When the 

 fiekls are approximately alike only one size letter may be used — 

 F ; when unlike, F will denote the largest sized areas, F medium 

 sized, f small sized When the areas are of but two sizes F and 

 f may be used. 



Arabic figHrc-^ following F, f, f, denote the number of teeth 

 borne by each field respectively; when the number is great (40 or 

 more) n is used to denote this fact. When in one and the same 

 gizzard the teeth are of different sizes this is indicated by use of 

 the marks ', ", '" ; ' denotes the largest sized teeth, " medium 

 sized, '" smallest sized. 



Wherever a gizzard consists of a repetition of similar fields, the 

 formula may be shortened by enclosing the repeated arrangement 

 within parentheses, and placing the proper coefficient before the 

 parenthesis to indicate the number of times the repetition occurs. 



When the same field contains two groups of teeth separated by 

 a distinct interval, these two groups are indicated in the formula 

 by placing one above the other with a horizontal line between them, 

 as in common fractions, the anterior group of teeth being repre- 



