Discussion

As an aid to the identification of the two species described in this account the type specimen of Psepdoxenomystax bulbiceps in the Australian National Museum, Sydney, has been kindly re-examined by Mr. G. P. Whitley for characters not included in the original description; specimens of Ariosoma balearica, a part of the material from which Smith made his description, were examined by Professor Smith in the Department of Ichthyology, Rhodes University, South Africa. These examinations supplemented the brief accounts of these two species in the literature.

Insignificant differences are revealed between the type of Pseudoxenomystax bulbiceps and New Zealand specimens of comparable length. The following are various body proportions in the type and in 14 New Zealand specimens (in brackets) head 6:8 (6:8–7:4), depth 19:8 (18.6–21.0) in total, eye 4.7 (4.7–5.2), snout 3.8 (3.0–4.1), cleft of mouth 3.4 (2.5–3.3), pectoral 3.4 (3.3–4.1), branchial aperture 6.3 (6.5–7.9) all in head, a-d percentage 23.6 (22.7–23.9) The type has 10 branchiostegal rays; the premaxillary patch of teeth is oval and about half the length of the vomerine patch which has four longitudinal rows; 47 pores lie before the level of the vent New Zealand specimens have 9–10 branchiostegals; the premaxillary patch of teeth is oval and contained two and a-half to three times in the length of the vomerine patch which has three to four rows; 43–48 pores lie before the level of the vent. The swollen; bulbous, spongy head which is so characteristic of the type is also well-marked in small New Zealand specimens. In these specimens also the lateral line pores have raised rims and lie low down on the lateral line ridge; exactly as in the type; larger specimens have the pores on the ends of short tubes; apparently an adult character. Epidermal processes cannot be detected in the type but neither can they be found in New Zealand specimens of a similar length although these structures exist in adult New Zealand material. Considering the close likeness thus displayed between this material and the single specimen described by Whitley the present author has no hesitation in referring the smaller New Zealand species to P. bulbiceps.

The large eels described here as Pseudoxenomystax hirsutus bear a striking resemblance in general body proportions and in the presence of epidermal processes to Ariosoma balearica as described and figured by Smith from the South African region. South African specimens collected at the same time as that described by Smith have simple epidermal processes; there are 14 rays in the pectoral, 300 in the dorsal, and 240 in the anal; the lateral line pores number 43 before the level of the vent and are carried on the ends of short tubes. In the New Zealand material the dorsal always begins over the branchial aperture. This is in contrast to Smith's specimens in which the origin of the dorsal usually lies at a level halfway along the pectoral. On this basis the New Zealand eels are considered distinct from the South African A. balearica and are described as a new species.

Pseudoxenomystax bulbiceps and P. hirsutus themselves display a remarkably close external similarity. It was only when the difference in the fin-ray counts was discovered that the two species became separable. In the 14 specimens of P. bulbiceps examined there are 327–353 rays in the dorsal, 240–258 in the anal and 16 in the pectoral, this may be compared with 306–314, 204–226 and 14–15 in P. hirsutus, the larger species at maturity. Lateral line pores before the level of the vent are 43–48 in P. bulbiceps, 39–44 in P. hirsutus, the pectoral fin and trunk are more slender in P. bulbiceps, while P. hirsutus has a wide pectoral and is a deepbodied bulky eel with correspondingly wider interbranchial and interorbital regions.