Praelongithyris Middlemiss 1959

Praelongithyris ? aff. borealis Owen, 1976

Fig. 7.9–7.20

1976 v. aff. “ Praelongithyris ” borealis new species—Owen, p. 11, pl. 2, fig. 2, text-fig. 6.

2011 v. ‘ Praelongithyris’ sp.—Hammer et al., p. 20, table 2.

Material and occurrence. Seep 1 (PMO 224.886?, PMO 224.912, PMO 224.907, PMO 224.908?), seep 9 (PMO 227.424–425, PMO 224.888–890, PMO 224.898), seep 12 (PMO 224.887?, PMO 224.935–936).

Description. Elongate rounded to sub-pentagonal outline with dorsal valve longer than wide, evenly biconvex profile with dorsal valve flatter, euseptoidum present, elongate adductor muscle scars. Rounded beak ridges. Lateral commissure gently arched, anterior commissure rectimarginate to incipiently or broadly uniplicate.

Discussion. The elongate outline and biconvex profile are comparable to “ Praelongithyris ” borealis Owen. As with Cyrtothyris discussed above, the Spitsbergen specimens reach larger dimensions than the material from Greenland. A uniplicate specimen with an elongate-oval outline (Fig. 7.17–7.20) resembles Moutonithyris moutoniana (d’Orbigny). A juvenile specimen (Fig. 7.13–7.16) is similar in outline to Cyrtothyris cyrta (Middlemiss 1976, pl. 7, fig. 5) although the profile of the latter has a less inflated dorsal valve; however, the generalized rounded outline is typical for juveniles of many terebratulide species.

Praelongithyris ? aff. borealis is similar in outline to Taimyrothyris kropotkini (Moisseiev) figured by Dagys (1968, pl. 23, fig. 3). The material recorded by Dagys reaches larger maximum dimensions than the largest Spitsbergen specimen, being L 48; W 34; T 29 mm (Dagys 1968, p. 128) and is more inflated in profile. It is difficult to be certain as to the affinities of the Spitsbergen material without the aid of details of internal structures. However the Spitsbergen specimens, where decorticated, show no trace of crural plates (that would be expected) adjoining the floor of the dorsal valve, typical of the Boreiothyrididae (as in Taimyrothyris, Dagys 1968, fig. 76) and it is concluded that the material is not referable to Taimyrothyris. Dagys recorded Taimyrothyris kropotkini from the Lower Volgian and questionably from the Callovian–Oxfordian. Owen (1976) recorded “ Praelongithyris ” borealis from the Valanginian of Falskebugt, Wollaston Forland, East Greenland. The Spitsbergen material comes from the Upper Ryazanian.

Stratigraphic and geographic distribution. Upper Ryazanian of Spitsbergen.