Abstract.

Sixty-Six species of digenetic trematodes are recorded from 58 species of New Zealand fishes. Thirty-eight new species and six new genera (five of them based on New Zealand species) are named. Comparative studies lead to the reduction of 11 previously named species as synonyms, and 9 new names are proposed as new combinations.

A tendency toward host specificity of these trematodes is seen in that 56 species, or about 80% of the total, were collected from single species of host, and only three species, all Hemiundae, were found in five or more species of host.

Some affinities are noted to trematodes of fishes of the Northern Hemisphere. Of the 25 species previously known outside of New Zealand: 17 species occur also in either the North Atlantic or the North Pacific; 11 species in the North Atlantic (9 being known only from there); 9 in the North Pacific (6 being known only from there); 7 in Australia or Tasmania, 3 in the Celebes. Several species of the cold water South Pacific are common in fishes of deep water in the Gulf of Mexico suggesting that a continuous distribution may occur by way of the deep sea. The fish hosts differ in the different regions. Derogenes varicus is a common trematode of New Zealand as it is in many fishes of the Northern Hemisphere and in deep sea fishes, although it is absent in warm seas. On the other hand, six of the eight trematodes of the conger eel, a fish of both hemispheres, are not known in the north.

Keys are given to species of seven genera (Decemtestis; Genolinea; Opecoelus; Plagioporus [subgenus Plagioporus]; Pseudopecoelus; Tergestia and Tubulovesicula).

A host-parasite list is given.