[K] There are several genera of flies of the family _Cordyluridæ_; (i.e. _Acalyptratæ_) which might be placed with the _Anthomyiidæ_ (i.e. _Calyptratæ_), owing to the relatively large size of their squamæ. As there is no single character which will satisfactorily separate all doubtful genera of these two groups we must arbitrarily fix the limits. In general those forms on the border line having a costal spine, or lower squama larger than the upper, or the lower surface of the scutellum more or less pubescent, or the eyes of the male nearly or quite contiguous, or the eyes hairy, or the frontal setæ decussate in the female; or any combination of these characters may at once be placed with the _Anthomyiidæ_. Those forms which lack these characteristics and have at least six abdominal segments (the first and second segments usually being more or less coalescent) are placed with the Acalyptrates. There are other acalyptrates with squamæ of moderate size which have either no vibrissæ, or have the subcosta either wholly lacking or coalescent in large part with R_1 or have spotted wings; they, therefore will not be confused with the calyptrates. [L] _Pachymyia_ Macq. is closely related to _Stomoxys_. It differs in having the arista rayed both above and below. _P. vexans_, Brazil. [M] The genus _Eudasyphora_ Town. has recently been erected to contain _D. lasiophthalma_. [N] _Nitellia_, usually included in this genus has the apical cell petiolate. _Apollenia_ Bezzi, has recently been separated from _Pollenia_ to contain the species _P. nudiuscula_. Both genera belong to the Eastern hemisphere. [O] The following three genera are not sufficiently well defined to place in this synopsis. In color and structural characters they are closely related to _Cynomyia_ from which they may be distinguished as follows. _Catapicephala_ Macq., represented by the species _C. splendens_ from Java, has the setæ on the facial ridges rising to the base of the antennæ and has median marginal macrochætæ on the abdominal segments two to four: _Blepharicnema_ Macq., represented by _B. splendens_ from Venezuela has bare genæ, oral setæ not ascending; tibiæ villose; claws short in both sexes; _Sarconesia_ Bigot with the species _S. chlorogaster_ from Chile, setose genæ; legs slender, not villose; claws of the male elongate. [P] _Plinthomyia_ Rdi. and _Hemigymnochæta_ Corti are related to _Ochromyia_, though too briefly described to place in the key. APPENDIX HYDROCYANIC ACID GAS AGAINST HOUSEHOLD INSECTS The following directions for fumigating with hydrocyanic acid gas are taken from Professor Herrick's circular published by the Cornell Reading Course: Hydrocyanic acid gas has been used successfully against household insects and will probably be used more and more in the future. It is particularly effective against bed-bugs, and cockroaches, but because _it is such a deadly poison it must be used very carefully_.