The Oxyuridae parasitic in Primates have a restricted host range with, in the wild, one species of parasite characteristic of one genus of host (Inglis, 1961). Under such conditions one would expect the hosts and their parasites to show parallel evolutionary trends. While this is not established in detail there is a broad correlation between the trends that can be established in the morphology of the parasites and the phylogenies of the hosts (Inglis, 1965).
Recently some parasites were reported which suggested that the Hapalidae could be considered primitive monkeys of the superfamily Ceboidea rather than specialized (Inglis & Dunn, 1964), but it was then stressed that, because few parasite records were available, the suggestion must be tentative. However, two further samples of pin-worms from Hapalidae have now become available which also support this suggestion. One sample is from Oedipomidas oedipus (reported by Menschel & Stroh (1963) as Enterobius minutus) and the other is from Callimico goeldii. Both samples represent new species which are described below.
The specimens from C. goeldii are particularly interesting because they represent a species which is clearly con-generic with those from the Hapalidae that have been studied. This suggests that Callimico should be referred to the family Hapalidae rather than to the family Cebidae or even, as is suggested by some authors, to a distinct family Callimiconidae.
Both the new species are referable to the genus Trypanoxyuris and the opportunity is taken to publish an illustration of the lateral view of the male tail of Trypanoxyuris callithricis (Fig. 1).