Phthanoncoceratidae Evans & King 1990

Order, gen. et sp. indet. A

Fig. 45C–D

Specimen FMNH-P30354, from Profilstranda section, Ny Friesland, Spitsbergen, bed PO 131, 128 m above base of Olenidsletta Member, V2 b trilobite zone, Blackhillsian, Floian.

Specimen FMNH-P30354 is a 30 mm long fragment of a phragmocone and part of a body chamber. The preserved part of the body chamber is 14 mm long and has a compressed conch cross section with rW = 0.9 at a height of 10 mm. The angle of expansion is not known with precision, but the conch is longiconic and its width grows less than 1 mm at the preserved length of 30 mm. The shell surface is smooth. The conch is nearly orthoconic or slightly curved with the siphuncle presumably near or at the conch margin. The direction of conch curvature is difficult to determine, because the specimen is slightly distorted taphonomically, but presumably the siphuncle is at the concave side of the conch curvature. The sutures are obliquely transverse and bent forward on the convex side of the shell. Approximately five to six chambers occur per length similar to the corresponding conch height. The chamber length is 1.8 mm at a conch height of 9.5 mm (0.19 of corresponding conch width).

This specimen is relatively well preserved externally, but the position of the siphuncle, its shape and the shape of the septal necks are unknown, which precludes any further determination. Based on the relatively narrow septal spacing and the almost straight slender conch form, the specimen is either a fragment of a bassleroceratid or a proterocameroceratid.