Dowlingoceras sp. B

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 : 72-73

Dowlingoceras sp. B

Fig. 27J

Material examined

ESTONIA • Paope quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 47-866.

Description

The specimen is a straight, slightly deformed (compressed) fragment of ca eight chambers of the phragmocone and a nearly complete mature body chamber. At the base of the body chamber, the conch diameter is 47 mm, the diameter slightly increases adorally over a distance of ca 20 mm to 60 mm, then continuously decreases to a diameter of 58 mm near the aperture. A shallow and wide constriction is present ca 20 mm from the peristome. The peristome is only partially preserved. The body chamber is ca 60 mm long.

The phragmocone increases in diameter from 42 mm to 57 mm at a length of 52 mm (angle of expansion 16°). The sutures are straight and directly transverse while traces of the siphuncle are present near the conch margin, which are too poorly preserved measure. The remaining traces suggest that the siphuncle was fusiform.

Remarks

The poor preservation of this specimen does not allow further determination. The conch shape combined with the subfusiform siphuncle identify the specimen as a Dowlingoceras .

Diestoceratidae gen. et sp. indet.

Fig. 27M

Material examined

ESTONIA • Salu; Pirgu Regional Stage; TUG 1745-192.

Description

The specimen is a fragment of a nearly straight mold of a mature body chamber and nine chambers of the phragmocone which is partially deformed. Parts of the shell are eroded. The conch surface is not preserved. The fragmentary preservation does not permit measurement of the original conch cross section. The maximum conch diameter (28 mm) is located at the base of the body chamber. The body chamber is ca 28 mm long with slightly convex conch margins, it contracts adorally to a diameter of ca 27 mm where a shallow, inconspicuous constriction is located ca 5 mm distant from the peristome. The phragmocone diameter increases from 23 mm to 27 mm at a length of 16 mm (angle of expansion = 18°). The sutures are directly transverse and 3.5 mm apart where the conch diameter is 27 mm (RCL = 0.13). On the surface of the phragmocone, faint longitudinal lirae may be seen.

Remarks

The conch shape, shape of the mature body chamber as well as spacing and pattern of sutures of this specimen are suggestive of a small diestoceratid. The small mature size and the relatively long body chamber are not known from any species of Danoceras , Dowlingoceras or Diestoceras described in the literature. However, as crucial features for determination, including the siphuncle position and shape, are not preserved, while the conch cross section cannot be fully be reconstructed, a genus and species level determination of this specimen is impossible.

Family Graciloceratidae Flower in Flower & Kummel, 1950