This paper presents the taxonomic results regarding the Chaetognatha collected during a voyage to the oceanic island of Trindade made in 1950. Collects were done at different stations around the island and in the waters above banks between the island and the continent. Seven different species were collected, 5 of which belong to the genus Sagitta: 8. bipunctata, 8. enflata, 8. friderici, 8. hexaptera, 8. serratodentata, one is recognized as a new species of the genus Pterosagitta: Pt. besnardi, and finally the last is Krohnitta subtilis. Descriptions and drawings are presented of the species, as well as records of what is known of their habits and of the environments which they select. The new species, Pterosagitta besnardi, the second known of this genus, is as a whole similar to its elder: Pt. draco; but differs from it in some essential points. Pt. besnardi is shorter, its caudal segment is proportionately shorter, it has a smaller number of teeth and hooks, the hook's sheath has no crest, it has intestinal diverticula, its receptacula are extremely large and have a clavate shape and, finally its vesiculae are short and oval. This work was done aiming at a better knowledge of the Chaetognathous fauna of the western south Atlantic and for this purpose more work is being prepared dealing with the coastal species. Random informations are being pieced together in the hope of gathering in the near future enough material to establish some useful indicator among the species of this group that might be efficiently used for practical purposes.
