Some years ago we received a collection of foraminifera-bearing samples from Dr. H. K. Kugler and Dr. E. Lehner for examination, in sequence to the collection of larger foraminifera already examined from Central Falcon (Venezuela). (See Nettie E. Gorter and I. M. van der Vlerk, L.G.M., Dl. IV, afl. 2, 1932, p. 94—122). The material from Trinidad is very rich in representatives of the Orbitoididae family. On a closer study of the different genera of this family, for which the large collection of Indian and European Orbitoididae in the National Geological Museum in Leiden provided ample material, we observed that for the determination of genus the interlocular canalsystem is the most important feature. In the Orbitoididae the plasma is conveyed through the equatorial plane by means of canals and stolons. The first complete description of this was given by H. J. Carter in the Annals of Nat. Hist., 3rd series, vol. VIII, p. 449—453. In this article he remarks that in Orbitoides there are always four stolons to each chamber, while in infiltrated specimens of Orbitolites (= Lepidocyclina) mantelli, he sometimes found ever 6. C. W. Gümbel, Abh. k. bayer. Ak. W., II, Cl, X, Bd. II, 1868, p. 673, pointed out that these stolons formed a system, which he calls an interlocular canalsystem in analogy to the „interseptal canalsystem” which runs through the septa of the chambers in most foraminifera, but which is absent in the Orbitoididae. To avoid confusion with this interseptal canalsystem which in the literature is called simply canalsystem, we thought it better to use the expression „stolonsystem” here. It now appears that this system differs in different groups of Orbitoididae. For the sake of brevity however we will here confine ourselves to the groups connected with the genera to be dealt with in this monograph.