STUDIES OF VARIATION IN INSECTS 311 



used as a diagnostic character, as shown in the following ex- 

 amples : 



Phenacoccus pcrgandei Ckll. (Psyche, 1896, supp., p. 19). 

 Formula: 3, 2, 1 (i, 4, 5, 6, 9), (7, 8). 



P. gossypi Ckll. (Jour. N. Y. Ent. Soc., 1898, Vol. VI, p. 

 170). Formula: 2, (3, 9), (i, 4, 5, 6, 7, 8). 



P. artemesice Ehr. (Canad. Ent., 1900, Vol. XXXII, p. 313). 

 Formula: 2, 3, 9, i, 4, (5,6, 7, 8). 



P. stachyos Ehr. (Canad. Ent., 1900, Vol. XXXII, p. 314). 

 Formula: 3, 2, (4, 5), 9, (i, 6), 7, 8. 



P. minimus Tins. (Canad. Ent., 1898, Vol. XXX, p. 223). 

 Formula: 9, (2, 3) i, 6, 7, (4, 5, 8). 



FIG. 79. Antenna (greatly enlarged) of the scale insect, Ceroputo yuccce, 

 with segments numbered. 



P. solenopis Tins. (Canad. Ent., 1898, Vol. XXX, p. 47). 

 Formula : 2, 9, 3, (i, 5) 4, (6, 7) 8. 



P. americdnce Ckll. (Canad. Ent., 1897, Vol. XXIX, p. 91). 

 Formula: 9, i, 3, 2, (8, 7), (4, 5,6). 



P. simplex King. (Ent. News, 1902, Vol. XIII, p. 42). 

 Formula: (3, 9), (i, 2), 8, 6, (5, 7), 4. 



P. ivilmattce Ckll. (Ann. and Mag. Nat. Hist., 1901, ser. 7, 

 Vol. VIII, p. 57). Formula: 2, 9, 3, i, 5, (4, 6, 7, 8). 



Ceroputo yuccce barberi Ckll. (Bull. 4, Tech. Series, Div. 

 Ent. U. S. Dept. Agric., p. 39). Formula : 9, 3, ( i, 2, 4, 5, 6, 



7,) 8. 



C. bahice Ehr. (Canad. Ent., 1900, Vol. XXXII, p. 314). 

 Formula: 3, 5, 9, 6, 7, 4, 8, i, 2. 



In the examination of the antennae of twenty-five female 

 individuals of Ceroputo (Pkenacoccus) yuccce (?) (if not yuccce 



1 Segments in parenthesis are of equal length. 



