. Bulletins of American paleontology. I 86 Bulletin ISO 232 Family TKOCHOLITIDAE Chapman, 1857 Genus ARKOtERAS Ulrich, Foerste, Miller and Furnish, 1942 Arkooeras sp. PI. 10, figs. 10-11; text fig. 18 A single fragment of a silicified phragmocone was available for study. It is too fragmentary to serve as the type of a new species. Description of specimen No. 357.—(Bureau of Mineral Re- sources, Geology and Geophysics, Canberra). The specimen is con- sidered to be part of a loosely coiled nautilicone, with an estimated maximum diameter of 15 mm. It is chambered throughout, has a length of 11 mm
. Bulletins of American paleontology. I 86 Bulletin ISO 232 Family TKOCHOLITIDAE Chapman, 1857 Genus ARKOtERAS Ulrich, Foerste, Miller and Furnish, 1942 Arkooeras sp. PI. 10, figs. 10-11; text fig. 18 A single fragment of a silicified phragmocone was available for study. It is too fragmentary to serve as the type of a new species. Description of specimen No. 357.—(Bureau of Mineral Re- sources, Geology and Geophysics, Canberra). The specimen is con- sidered to be part of a loosely coiled nautilicone, with an estimated maximum diameter of 15 mm. It is chambered throughout, has a length of 11 mm., and represents about one-third of a volution. The whorl is compressed and oval in cross-section, the dorsum being slightly more narrowly rounded than the venter. The dorso- ventral and lateral diameters at the posterior end of specimen meas- ure mm. and mm. respectively. The corresponding diameters at the anterior end are mm. and mm. The siphuncle is mod- erately large, compressed, and situated close to, but not in contact with, the dorsal shell wall. At the anterior end of the specimen the siphuncle has a dorso-ventral diameter of .7 mm., a lateral diameter of .5 mm., and its dorsal margin is situated .2 mm. from the dorsum. The sutures are simple and represent a direct reflection of the shell cross-section. A shallow dorsal saddle is separated by a pair of shallow rounded lateral lobes from a higher saddle across the venter. The shell is smooth. Comparisons.—Arkoceras, Cyclolituites, and Wichitoceras are the only members of the Trocholitidae which are not dorsally im- pressed. The specimen described above has affinities with both Arko-. Fig. 18. Cross-section of Arkoceras sp., X 6J^.. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Paleontological Research Institution (Ithaca, N. Y.
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