Cochlioceras roemeri Dzik, 1984 from Baltic erratic boulders, Poland; restoration of adult conch based on specimens from boulder E-252, Rozewie (a), longitudinal section of the siphuncle (b) and cameral and siphuncular deposits of ZPAL N/001 (f). Cochlioceras burchardi (Dewitz, 1880) from Baltic erratic boulders; restoration of adult conch based mostly on specimens from boulder E-149, Międzyzdroje (d) and longitudinal section of the siphuncle (e) 

Cochlioceras roemeri Dzik, 1984 from E. reclinatus Zone, Lasnarnagian, Rozewie, Poland;

1. Medial section through adapical part of a phragmocone, ZPAL N/OO4.

2. Medial section through adapical part of a phragmocone, ZPAL NjOOl ; supposedly Volkhovian, Rozewie, Poland; x 3.

3. Adult specimen in lateral (a) and ventral (b) views, ZPAL N/OO9.
4. Medial section through a phragmocone, ZPAL N/Oll; erratic boulder E-262, E. ree/inatus Zone, Lasnarnagian, Miedzyzdroje, Poland.

5. Medial section through a phragmocone (a, b), holotype, ZPAL N/OlO ; x 2.

6. Medial section through a phragmocone, ZPAL N/OO6; note small diameter of the apical part.

Diagnoza

Ventral siphuncle up to one third of the shell in diameter, filled with deposits in its apical part; siphuncular deposits in form of massive rod at ventral side, with flat rings at septal necks; cameral deposits well developed.

Porównanie

C. roemeri Dzik, 1984. does not differ externally from its congeners. Its uniqueness consists in its much wider siphuncle. It differs from C. burchardi also in its siphuncle lying a little away from the shell wall and, consequently, in its straight septal suture. Any comparison to the siphuncular structure of other congeneric species is impossible because of lack of data.

A similar siphuncular structure was recorded among the American baltoceratids (FLOWER 1964).

Autekologia

Występowanie geograficzne

Zasięg czasowy

C. roemeri Dzik, 1984 occurs rather commonly in erratic boulders of the E. reclinatus Zone (Folkeslunda Limestone), but never in association with its coeval congener, C. burchardi.
Provided that the specimens assigned by BALASCHOV (1968) to Proterocameroceras
gdovense (except for the holotype supposedly being the apical part of a shell of Dideroceras)belong to C. roemeri, the latter species occurs also in the E. reclinatus Zone of Estonia. The conspecificity of "P. gdovense" and C. roemeri is indicated by the shell shape and presumably also the structure of siphuncular deposits (see BALASCHOV 1968, pI. 1: 2v). One specimen was found in a boulder indistinguishable in lithology from those of the Paroistodus originalis Zone(untere rote Vaginatenkalk; Volkhovian); anyway, this specimen cannot be younger than the Kundan.

Materiały muzealne

Literatura

Dzik, J. 1984a. Phylogeny of the Nautiloidea. Palaeontologia Polonica 45, 1-255