BRITISH AVONIAN CONODONT FAUNAS 215 
1949 Pseudopolygnathus cf. crenulata E. R. Branson ; Thomas: 412, Pl. 4, fig. 18. 
1949 Pseudopolygnathus constrictiterminata Thomas : 428, Pl. 4, fig. 16. 
1949 Pseudopolygnathus cf. P. asymmetrica E. R. Branson ; Thomas: 436, Pl. 3, fig. 42. 
1951 Pseudopolygnathus prima Branson & Mehl ; Hass: 2358, Pl. 1, fig. 11. 
1957 Pseudopolygnathus prima Branson & Mehl ; Cloud, Barnes & Hass : 813, Pl. 5, fig. ro. 
1957 Pseudopolygnathus ivvegularis Branson ; Bischoff : 51, Pl. 6, figs. 12, 13. 
1957 Pseudopolygnathus dentilineata E. R. Branson ; Bischoff: 50, 51, Pl. 4, fig. 29 only. 
1959 Pseudopolygnathus prima Branson & Mehl; Hass: PI. 49, fig. 27. 
1959 Spathognathodus cf. costatus (E. R. Branson) Voges : 298, 299, Pl. 34, fig. 48 only. 
1966 Pseudopolygnathus prima Branson & Mehl; Klapper: 14, Pl. 4, fig. 8. 
MATERIAL. 64 specimens : figured, X 546, X 497, X 498, X 499, X 500, X 540. 
RANGE. Avon Gorge Z 13-Z 28. 
DESCRIPTION. This species is extremely variable. All forms with an asym- 
metrical platform, a narrow row of nodes or ridges on the right and left sides, but 
with a flared anterior portion on the left, are referred to it. The basal cavity, accord- 
ing to Klapper, is narrower than the platform, but not all our specimens of P. primus 
agree with this. 
The axis is arched, and right and left forms have been found which are bilaterally 
asymmetrical elements. The platform is more strongly developed on the right side 
than on the left in both right and left forms. The outer margin of the right side of 
the platform is convexly curved and bears at least 7 nodes or ridges. The right side 
of the platform is widest at mid-length, and tapers uniformly to the anterior and 
posterior. The shorter left side of the platform consists of a smaller number of 
nodes or ridges than the right side. The carina consists of fused denticles for the 
greater part of its length, but there are a few distinct denticles at the posterior 
extremity, where the carina is extended a short distance beyond the posterior end of 
the platform. 
The basal cavity is situated near the mid third of the unit, and is sub-circular in 
outline with a fold on the inner margin and with a convex outer margin. A narrow 
groove extends from the anterior extremity of the basal cavity to the posterior 
extremity of the unit. The anterior edge of the unit, anterior to the basal cavity, 
is sharp. 
REMARKS. Pseudopolygnathus primus is similar in outline to P. dentilineatus, but 
the platform ornamentation in the two species is different. The platform ornamen- 
tation of P. primus has at least seven nodes or ridges on the right side, and ridges are 
frequently present, whereas in Pseudopolygnathus dentilineatus there are nearly always 
nodes which are confined to the margin ; ridges are rare and eight nodes or ridges on 
the right side of the platform are unknown. Both margins of the platform in P. 
dentilineatus are convex. InP. primus the margin of the left side of the platform is 
more angular at the anterior than that of P. dentilineatus. 
The development of P. primus has been described by Voges (1959) and again by 
Klapper (1966). The writers agree with the opinion of Klapper (1966: 14) that 
there is a wide variety of surface ornamentation in P. primus, but that this can be 
regarded as intraspecific variation. 
