Palaeodawsonocerina, Kroger & Isakar, 2006

Kröger, Björn, 2025, The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia, European Journal of Taxonomy 978, pp. 1-169 : 33-34

Palaeodawsonocerina ? sp.

Fig. 12K

Material examined

ESTONIA • 1 spec.; Hosholm shore; Adila Formation, Pirgu Regional Stage; TUG 939-78 .

Description

The specimen is a ca 39 mm long, 18–20 mm high, orthoconic fragment (angle of expansion 3°) of a phragmocone with well-preserved shell sculpture. The conch cross section is slightly deformed. The conch is annulated with ca four annulations in a distance equal to the corresponding conch cross section. The annulations are directly transverse. The conch is ornamented with ca 60 fine longitudinal lirae around the circumference and subordinate transverse growth lines or lirae, producing a reticulate pattern (ca 10 transverse lirae per annulation). The septa are only partially preserved, the siphuncle and septal necks are not preserved. The sutures are positioned in the troughs of the annulations and are directly transverse parallel to the annulations.

Remarks

The finely reticulate ornamentation and the general conch shape of this specimen is similar to other species assigned to P. senckenbergi . It differs from the latter in having a wider spacing of its longitudinal lirae (1 mm and 60 lirae around circumference versus five to seven lirae per mm in P. senckenbergi ). The fragmentary preservation of the internal characters leaves the genus level determination questionary because a similar fine reticulate ornamentation is known from Anaspyroceras , and Gorbyoceras (see e.g., Flower 1943b). Possibly, the specimen belongs to the same species as a specimen described by Strand (1934: 21) under G. clathratoannulatum , also ornamented with ca 60 longitudinal lirae.

Order Pseudorthocerida Flower & Caster, 1935

Family Proteoceratidae Flower, 1962