486 J- P- J- Ravn. 



(55. Cardioceras alternans v. Buch sp. 

 PL XXXVI, figs. 1, 2 and 3. 



(1831) 1885. Ammonites alternans v. Buch, Petrifications remarquables. p. 145; PI. 18, 



fig. 4. 



1845. Ammonites subeordatus d'Orbic.ny, in Murchison, Verneuii. et Keyseri.ing, Geo- 



logie de la Russie d'Europe. II. p. 434; 

 PI. 34, figs. 6—7. 



1846. alternans v. Buch ; Keyseri.ing, Petschora-Land. p. 323, PL 22, fig. 2. 

 1849. — — — , Quenstedt, Die Cephalopoden. p. 96; PI. 5, figs. 



7—8. 

 — — — , Rouillier, Etudes progr. Geologie de Moscou. V. 



p. 362; PI. L, fig. 88; PI. M, fig. 109. 

 1878. Amaltheus alternans Buch; Nikitin, Group of Amaltheus funiferus Phill. p. 148; 



PI. 2, fig 18. 

 1881. — — — ; Nikitin, Jura-Ablagerungen an der oberen Wolga. 



p. 59. 

 1904. Cardioceras — — ; Ilovai'sky, L'Oxfordien et le Sequanien etc. p. 272; 



PI. 11, figs. 6-7. 



Some specimens of this extremely variable species were found 

 in "Kloft I" on Store Koldewey Island in the blue-gray, calcareous 

 and micaceous sandstone. They are all more or less imperfect and 

 in part much compressed. A well-preserved and practically complete 

 imprint shows short, but well-marked ribs only in the neighbourhood 

 of the external side on the beginning of the last of the whorls pre- 

 served, but the sides are smooth ; later, ribs also appear on the edge 

 of the umbilicus; these ribs become stronger and stronger, continuing 

 over the side and in the end joining on to the first-mentioned ribs, 

 which at the end curve strongly forwards and disappear before 

 reaching the ridge, so that the latter is bounded on each side by a 

 smooth band. The number of ribs externally is almost double that 

 on the umbilical margin, as a short rib is as a rule inserted on the 

 outside towards the periphery between each two of the ribs, which 

 start from the umbilical edge. The latter ribs show more or less 

 distinctly a thickening, which lies almost midway on the side, though 

 a little nearer the external side. The ridge is very finely dentated. 

 The greatest diameter of this specimen is 31 mm and the greatest 

 height of the whorl 14 mm. In the whole of its sculpture it shows 

 a considerable resemblance to the specimens of C. Volgae Pavl., 

 described by P. (i. Khause and found in the Kimmeridgian in East 

 Prussia; 1 but it is distinct from this in that especially the insertion 

 of the secondary ribs is more regular and the dentation of the ridge 

 much finer. 



In addition to Ibis specimen we have a couple of compressed 



1 P. G. Khause: Ueber Diluvium, Tertiar, Kreide und Jura in der Heilsberger 

 Tiefbobrung. p. 241; PI. 3, figs. 1—4. — Jahrb. Preuss. geolog. Landesanst. 

 Bd. 29. Berlin 1908. 



