The material for this paper was forwarded to the author by Dr. Guy Marshall, of the Imperial Bureau of Entomology, and was collected by Mr. C. B. Williams.

The insects were said by him to be parasitic on a Cercopid of the genus Clastoptera, which was found attacking cacao trees. This highly unusual habit gives much interest to the species. Unfortunately the number of individuals sent was quite inadequate to enable one to deal satisfactorily with such small and obscure insects, especially as shrivelling takes place to a different extent in various individuals, which renders the provision of a reasonably large number more necessary than in more normal forms of fly. The individuals sent included three pinned ones of a species from Trinidad (West Indies), and one pinned one of a species from Panama, together with the fragments of two others of the latter species in spirit. In spite of the paucity of material, it was felt to be desirable to put on record as fair a description as could be made under the circumstances. Two of the individuals of the Trinidad species were of one sex, and the third was apparently the other sex of the same species. The two former had all the appearance of representing the male, having brighter eyes, darkened wings, and the general facies of that sex. The genitalia were small and hidden in a terminal hood, such as is found in Drosophila melanogaster and Leucophenga maculata, but it was smaller than in either of these, even than in the latter, in which the hood is only moderately open at the tip, while widely so in the former.