Robertson — Flowers and Insects. 463 
ab.; (13) H. eS Nyl. 9, 8. and c. p., ab.; (14) H. confusus Sm. 9, s. 
and c. p.,ab.; (15) H. stultus Cr. 9, s. and c. p.,ab.; (16) Sphecodes 
sehen Rob. 9,8 
era aRiapibase (17) Empis sp., s.; Syrphidae: (18) Chrysogaster 
bitiaa gos (19) Platychirus quadratus Say; (20) P. hyperboreus Staeg.; 
(21) SexGorapia geminata Say; (22) M. marginata Say; (23) Sphaerophoria 
cylindrica Say; (24) Eristalis aeneus F.— alls, and f. p.; Tachinidae: (25) 
Gonia frontosa Say, s., ab.; (26) Phorocera ewcaat Will.; Sarcophagidae: 
(27) Sarcophaga sp.; (28) Cynomyia sp.; Muscidae: (29) Cyrtoneura sp. ; 
(80) Lucilia cornicina F.; Anthomyidae: (31) natant sp.; (32 and 33) 
Chortophila spp. Oscinidae: (84) Chlorops sp.— all s. or 
Lepidoptera — Rhopalocera: (85) Pyrameis huntera F: * (88) Nisoniades 
brizo B.— L.; Heterocera: (37) Diksierla erechtea Cram. 
Coleoptera — Oedemeridae: (38) Asclera ruficollis Say, f. p. 
SILPHIUM INTEGRIFOLIUM Michx.— The plant is common on 
prairies, grows from one to two metres high, and bears yellow 
heads which expand about four or five centimetres. 
The ray-flowers are female; those of the disc, male. The 
disc-flowers have a long, undivided hairy style which serves to 
expose the pollen to the visitors. Nectar is secreted by the 
dise flowers, which have tubes six or seven millimetres long. 
This places the nectar beyond the reach of short-tongued 
insects. 
The flowers bloom from July 9 to September 7. The visitors 
were observed on July 13, 14, 19, 28, and August 9: — 
Hymenoptera — Apidae: ( 7. Apis mellifica L. 8, S., one; fe Melissodes 
dentiventris Sm. , s., freq.; (3) M. aurigenia Cr. <j, s., freq.; (4) M. 
obliqua Say 6O', 8.3 (5) cruise dupla Say 9, s., freq.; (6) Lae pug- 
nata Say ¢'9,s. and c. p., ab.; (7) M. inimica Cr. i’, 8.; (= M. sayi Cr.); 
(8) M. montivaga Cr. J, s (9) M. petulans Cr. J), 8., tg. (10) = brevis 
Say g', s.; (11) Epeotiis, ceiegaits F. 3, s.; (12) E. lunatus Say <j, s.; 
Andrenidae: i Halictus ligatus Say Q, s.; (14) Agapostemon viridula F. 
of a2 S.andc 
Diptera — Bombylidae: Sr Systoechus vulgaris Lw., s.; Tachinidae: (16) 
Cistogaster occidua WIik., 
SILPHiIum Lacrinratum L.— Visitors —July 16, 18, 20, 25, 
and August 4:— 
Hymenoptera — Apidae: (1) Apis mellifica - 8 , 8.; (2) Bombus separa- 
tas Cr. 89, s., (3) B. americanorum F. 8, 8.; (4) Melissodes aurigenia 
Cr. ao 4, 8. ab.; (5) M. coloradensis Cr. <j’, 8. op ) M. bimaculata Lep. <j, 
8-5 (7) Ceratina dupla Say 9, s.; (8) Mezachile brevis Say 9, s-; (9) M. 
pugnata Say 9, s. and c. p.; (10) Epeolus remigatus F. ¢j', s.; Andrenidae: 
